 
 Gibt es einen Grund, warum die Bücher ohne Autor dort eingeordnet sind, wo sie es momentan sind? Es kommt mir komisch vor, da eins der beiden Werke unter G einsortiert ist, während ein anderes unter H steht.

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
      \pernottype{set}
      \step[notfield=translator, final]
      \step[notfield=editor, final]
      \step[fieldset=author, fieldvalue={\string{o\noexpand\adddot\addabbrvspace V.\string}}]
    }
    \map{
      \pernottype{online}
      \step[fieldset=location, fieldvalue={o\noexpand\adddot \addabbrvspace O\noexpand\adddot}]
    }
  }
}\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
      \pernottype{set}
      \step[notfield=translator, final]
      \step[notfield=editor, final]
      \step[fieldset=author, fieldvalue={\string{o.\noexpand\,V\noexpand\adddot\string}}, final]
      \step[fieldset=sortname, fieldvalue={zzzzzzzzz}]
    }
    \map{
      \pernottype{online}
      \step[fieldset=location, fieldvalue={o.\noexpand\,O\noexpand\adddot}]
    }
  }
}

 
 \documentclass[12pt, a4paper, ngerman, 
  toc=chapterentrydotfill, bibliography=totoc, 
  listof=nochaptergap, listof=totoc, 
  captions=figureheading, hidelinks,  fleqn]{scrreprt} 
\usepackage[T1]{fontenc} 
\usepackage[utf8]{inputenc} 
\usepackage[ngerman]{babel} 
\usepackage[onehalfspacing]{setspace} 
\usepackage{lipsum} 
\usepackage[a4paper, 
  left=4cm, right=2cm, top=1.5cm, bottom=2cm, 
  headsep=2cm, headheight=0.5cm, includehead=true, 
  footskip=0cm, includefoot=true, ]{geometry} 
\usepackage[autostyle, german=guillemets]{csquotes} 
\usepackage[backend=biber, style=ext-authoryear, 
  isbn=false, 
  maxcitenames=2, maxbibnames=999, 
  mergedate=false, 
  innamebeforetitle, dashed=false, 
  autocite=footnote, mincrossrefs=1]{biblatex} 
  
\usepackage{filecontents} 
\begin{filecontents*}{\jobname.bib} 
@online{test1Mit, 
  author  = {Artur Autor}, 
  title   = {Internetquelle mit Datum}, 
  url     = {http://example.edu/~elk/bronto.pdf}, 
  urldate = {2018-03-26}, 
  date 	  = {2000},
  usera   = {Test Stichwort1} ,
} 
@online{test1Ohne, 
  author  = {Artur Autor}, 
  title   = {Internetquelle ohne Datum}, 
  url     = {http://example.edu/~elk/bronto.pdf}, 
  urldate = {2018-03-26}, 
  usera   = {Test Stichwort2},
} 
@book{test2Mit, 
  author    = {Artur Autor}, 
  title     = {Buch mit Datum}, 
  edition   = {1}, 
  usera     = {Test Stichwort3}, 
  publisher = {FOMVerlag}, 
  location  = {Essen}, 
  date      = {2000}
}
@book{test2Ohne, 
  author    = {Artur Autor}, 
  title     = {Buch ohne Datum}, 
  edition   = {1}, 
  usera     = {Test Stichwort4}, 
  publisher = {FOMVerlag}, 
  location  = {Essen}, 
}
\end{filecontents*} 
  
  
\renewcommand*{\bibfont}{\normalfont\normalsize\singlespacing} 
\setlength{\bibinitsep}{.5\baselineskip} 
\setlength\bibhang{1cm} 
\DeclareLabeldate{% 
  \field{date} 
  \field{year} 
  \field{eventdate} 
  \field{origdate} 
  \literal{nodate} 
} 
\renewcommand*{\finentrypunct}{} 
\renewcommand*{\newunitpunct}{\addcomma\space} 
\DeclareDelimFormat[bib,biblist]{nametitledelim}{\addcolon\space} 
\DeclareDelimFormat{titleyeardelim}{\newunitpunct} 
\renewcommand*{\mkbibnamefamily}{\mkbibemph} 
\renewcommand*{\mkbibnamegiven}{\mkbibemph} 
\renewcommand*{\mkbibnamesuffix}{\mkbibemph} 
\renewcommand*{\mkbibnameprefix}{\mkbibemph} 
\DeclareDelimAlias{finalnamedelim}{multinamedelim} 
\DeclareNameFormat{family-given:init}{% 
  \usebibmacro{name:family-given} 
    {\namepartfamily} 
    {\namepartgiveni} 
    {\namepartprefix} 
    {\namepartsuffix}% 
  \usebibmacro{name:andothers}} 
\DeclareNameAlias{default}{family-given} 
\DeclareNameAlias{sortname}{default} 
\DeclareNameAlias{labelname}{family-given:init} 
\DeclareFieldFormat{editortype}{\mkbibparens{#1}} 
\DeclareDelimFormat{editortypedelim}{\addspace} 
\DeclareFieldFormat{translatortype}{\mkbibparens{#1}} 
\DeclareDelimFormat{translatortypedelim}{\addspace} 
\DeclareDelimFormat[bib,biblist]{innametitledelim}{\addcomma\space} 
\DeclareFieldFormat*{citetitle}{#1} 
\DeclareFieldFormat*{title}{#1} 
\DeclareFieldFormat*{booktitle}{#1} 
\DeclareFieldFormat*{journaltitle}{#1} 
\newbibmacro*{organization+location}[1]{% 
  \printlist{location}% 
  \setunit*{\locdatedelim}% 
  \printlist{organization}% 
  \newunit} 
\usepackage{xpatch} 
\xpatchbibdriver{online} 
  {\usebibmacro{organization+location+date}} 
  {\usebibmacro{organization+location}} 
  {}{} 
\DeclareFieldFormat[online]{date}{\mkbibparens{#1}} 
\DeclareFieldFormat{url}{<\url{#1}>}% oder {$\langle$\url{#1}$\rangle$} oder \textlangle/\textrangle 
\DeclareFieldFormat{urldate}{\mkbibbrackets{\bibstring{urlseen}\addcolon\space#1}} 
\renewbibmacro*{url+urldate}{% 
  \usebibmacro{url}% 
  \ifentrytype{online} 
    {\setunit{\addspace}% 
     \usebibmacro{date}} 
    {}% 
  \iffieldundef{urlyear} 
    {} 
    {\setunit*{\addspace}% 
     \usebibmacro{urldate}}} 
\renewbibmacro*{date+extradate}{% 
  \printtext[parens]{% 
    \printfield{usera}% 
    \setunit{\printdelim{titleyeardelim}}% 
    \printlabeldateextra}} 
\DefineBibliographyStrings{german}{ 
  nodate    = {{}o.\adddot \addabbrvspace J\adddot}, 
  andothers = {et\addabbrvspace al\adddot}, 
  urlseen   = {Zugriff}, 
} 
\DeclareSourcemap{ 
  \maps[datatype=bibtex]{ 
    \map{ 
      \pernottype{set} 
      \step[notfield=translator, final] 
      \step[notfield=editor, final] 
      \step[fieldset=author, fieldvalue={\string{o.\noexpand\,V\noexpand\adddot\string}}, final] 
      \step[fieldset=sortname, fieldvalue={zzzzzzzzz}] 
    } 
    \map{ 
      \pernottype{online} 
      \step[fieldset=location, fieldvalue={o.\noexpand\,O\noexpand\adddot}] 
    } 
  } 
}
\renewbibmacro*{cite}{% 
  \iffieldundef{shorthand} 
    {\ifthenelse{\ifnameundef{labelname}\OR\iffieldundef{labelyear}} 
       {\usebibmacro{cite:label}% 
        \setunit{\printdelim{nonametitledelim}}} 
       {\printnames{labelname}% 
        \setunit{\printdelim{nametitledelim}}}% 
     \printfield{usera}% 
     \setunit{\printdelim{titleyeardelim}}% 
     \usebibmacro{cite:labeldate+extradate}} 
    {\usebibmacro{cite:shorthand}}} 
\renewbibmacro*{postnote}{% 
  \setunit{\postnotedelim}% 
  \iffieldundef{postnote} 
    {\printtext{o\adddot\addabbrvspace S\adddot}} 
    {\printfield{postnote}}} 
%--------------- 
\addbibresource{\jobname.bib} 
  
\begin{document} 
\cite{test1Mit}\\
\cite{test1Ohne}\\
\cite{test2Mit}\\
\cite{test2Ohne}
\printbibliography[nottype=online]
\printbibliography[type=online,title={Internetquellen}]
\end{document}
\renewbibmacro*{date}{%
  \usebibmacro{bbx:ifmergeddate}
    {}
    {\iffieldundef{year}
       {\printtext[date]{\bibstring{nodate}}}
       {\printdate}}}\documentclass[12pt, a4paper, ngerman,
  toc=chapterentrydotfill, bibliography=totoc,
  listof=nochaptergap, listof=totoc,
  captions=figureheading, hidelinks,  fleqn]{scrreprt}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage[onehalfspacing]{setspace}
\usepackage{lipsum}
\usepackage[a4paper,
  left=4cm, right=2cm, top=1.5cm, bottom=2cm,
  headsep=2cm, headheight=0.5cm, includehead=true,
  footskip=0cm, includefoot=true, ]{geometry}
\usepackage[autostyle, german=guillemets]{csquotes}
\usepackage[backend=biber, style=ext-authoryear,
  isbn=false,
  maxcitenames=2, maxbibnames=999,
  mergedate=false,
  innamebeforetitle, dashed=false,
  autocite=footnote, mincrossrefs=1]{biblatex}
 
\usepackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@online{test1Mit,
  author  = {Artur Autor},
  title   = {Internetquelle mit Datum},
  url     = {http://example.edu/~elk/bronto.pdf},
  urldate = {2018-03-26},
  date      = {2000},
  usera   = {Test Stichwort1} ,
}
@online{test1Ohne,
  author  = {Artur Autor},
  title   = {Internetquelle ohne Datum},
  url     = {http://example.edu/~elk/bronto.pdf},
  urldate = {2018-03-26},
  usera   = {Test Stichwort2},
}
@book{test2Mit,
  author    = {Artur Autor},
  title     = {Buch mit Datum},
  edition   = {1},
  usera     = {Test Stichwort3},
  publisher = {FOMVerlag},
  location  = {Essen},
  date      = {2000}
}
@book{test2Ohne,
  author    = {Artur Autor},
  title     = {Buch ohne Datum},
  edition   = {1},
  usera     = {Test Stichwort4},
  publisher = {FOMVerlag},
  location  = {Essen},
}
\end{filecontents*}
 
 
\renewcommand*{\bibfont}{\normalfont\normalsize\singlespacing}
\setlength{\bibinitsep}{.5\baselineskip}
\setlength\bibhang{1cm}
\DeclareLabeldate{%
  \field{date}
  \field{year}
  \field{eventdate}
  \field{origdate}
  \literal{nodate}
}
\renewcommand*{\finentrypunct}{}
\renewcommand*{\newunitpunct}{\addcomma\space}
\DeclareDelimFormat[bib,biblist]{nametitledelim}{\addcolon\space}
\DeclareDelimFormat{titleyeardelim}{\newunitpunct}
\renewcommand*{\mkbibnamefamily}{\mkbibemph}
\renewcommand*{\mkbibnamegiven}{\mkbibemph}
\renewcommand*{\mkbibnamesuffix}{\mkbibemph}
\renewcommand*{\mkbibnameprefix}{\mkbibemph}
\DeclareDelimAlias{finalnamedelim}{multinamedelim}
\DeclareNameFormat{family-given:init}{%
  \usebibmacro{name:family-given}
    {\namepartfamily}
    {\namepartgiveni}
    {\namepartprefix}
    {\namepartsuffix}%
  \usebibmacro{name:andothers}}
\DeclareNameAlias{default}{family-given}
\DeclareNameAlias{sortname}{default}
\DeclareNameAlias{labelname}{family-given:init}
\DeclareFieldFormat{editortype}{\mkbibparens{#1}}
\DeclareDelimFormat{editortypedelim}{\addspace}
\DeclareFieldFormat{translatortype}{\mkbibparens{#1}}
\DeclareDelimFormat{translatortypedelim}{\addspace}
\DeclareDelimFormat[bib,biblist]{innametitledelim}{\addcomma\space}
\DeclareFieldFormat*{citetitle}{#1}
\DeclareFieldFormat*{title}{#1}
\DeclareFieldFormat*{booktitle}{#1}
\DeclareFieldFormat*{journaltitle}{#1}
\newbibmacro*{organization+location}[1]{%
  \printlist{location}%
  \setunit*{\locdatedelim}%
  \printlist{organization}%
  \newunit}
\usepackage{xpatch}
\xpatchbibdriver{online}
  {\usebibmacro{organization+location+date}}
  {\usebibmacro{organization+location}}
  {}{}
\DeclareFieldFormat[online]{date}{\mkbibparens{#1}}
\DeclareFieldFormat{url}{<\url{#1}>}% oder {$\langle$\url{#1}$\rangle$} oder \textlangle/\textrangle
\DeclareFieldFormat{urldate}{\mkbibbrackets{\bibstring{urlseen}\addcolon\space#1}}
\renewbibmacro*{url+urldate}{%
  \usebibmacro{url}%
  \ifentrytype{online}
    {\setunit{\addspace}%
     \usebibmacro{date}}
    {}%
  \iffieldundef{urlyear}
    {}
    {\setunit*{\addspace}%
     \usebibmacro{urldate}}}
\renewbibmacro*{date+extradate}{%
  \printtext[parens]{%
    \printfield{usera}%
    \setunit{\printdelim{titleyeardelim}}%
    \printlabeldateextra}}
\renewbibmacro*{date}{%
  \usebibmacro{bbx:ifmergeddate}
    {}
    {\iffieldundef{year}
       {\printtext[date]{\bibstring{nodate}}}
       {\printdate}}}
\DefineBibliographyStrings{german}{
  nodate    = {{}o.\adddot \addabbrvspace J\adddot},
  andothers = {et\addabbrvspace al\adddot},
  urlseen   = {Zugriff},
}
\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
      \pernottype{set}
      \step[notfield=translator, final]
      \step[notfield=editor, final]
      \step[fieldset=author, fieldvalue={\string{o.\noexpand\,V\noexpand\adddot\string}}, final]
      \step[fieldset=sortname, fieldvalue={zzzzzzzzz}]
    }
    \map{
      \pernottype{online}
      \step[fieldset=location, fieldvalue={o.\noexpand\,O\noexpand\adddot}]
    }
  }
}
\renewbibmacro*{cite}{%
  \iffieldundef{shorthand}
    {\ifthenelse{\ifnameundef{labelname}\OR\iffieldundef{labelyear}}
       {\usebibmacro{cite:label}%
        \setunit{\printdelim{nonametitledelim}}}
       {\printnames{labelname}%
        \setunit{\printdelim{nametitledelim}}}%
     \printfield{usera}%
     \setunit{\printdelim{titleyeardelim}}%
     \usebibmacro{cite:labeldate+extradate}}
    {\usebibmacro{cite:shorthand}}}
\renewbibmacro*{postnote}{%
  \setunit{\postnotedelim}%
  \iffieldundef{postnote}
    {\printtext{o\adddot\addabbrvspace S\adddot}}
    {\printfield{postnote}}}
%---------------
\addbibresource{\jobname.bib}
 
\begin{document}
\cite{test1Mit}
\cite{test1Ohne}
\cite{test2Mit}
\cite{test2Ohne}
\printbibliography[nottype=online]
\printbibliography[type=online,title={Internetquellen}]
\end{document}
alldates=ymd, labeldate=year,
\documentclass[12pt, a4paper, ngerman,
  toc=chapterentrydotfill, bibliography=totoc,
  listof=nochaptergap, listof=totoc,
  captions=figureheading, hidelinks,  fleqn]{scrreprt}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage[onehalfspacing]{setspace}
\usepackage{lipsum}
\usepackage[a4paper,
  left=4cm, right=2cm, top=1.5cm, bottom=2cm,
  headsep=2cm, headheight=0.5cm, includehead=true,
  footskip=0cm, includefoot=true,]{geometry}
\usepackage[autostyle, german=guillemets]{csquotes}
\usepackage[backend=biber, style=ext-authoryear,
  isbn=false,
  maxcitenames=2, maxbibnames=999,
  mergedate=false,
  innamebeforetitle, dashed=false,
  autocite=footnote, mincrossrefs=1,
  alldates=ymd, labeldate=year,]{biblatex}
 
\renewcommand*{\bibfont}{\normalfont\normalsize\singlespacing}
\setlength{\bibinitsep}{.5\baselineskip}
\setlength\bibhang{1cm}
\DeclareLabeldate{%
  \field{date}
  \field{year}
  \field{eventdate}
  \field{origdate}
  \literal{nodate}
}
\renewcommand*{\finentrypunct}{}
\renewcommand*{\newunitpunct}{\addcomma\space}
\DeclareDelimFormat[bib,biblist]{nametitledelim}{\addcolon\space}
\DeclareDelimFormat{titleyeardelim}{\newunitpunct}
\renewcommand*{\mkbibcompletename}{\mkbibemph}
\DeclareDelimAlias{finalnamedelim}{multinamedelim}
\DeclareNameFormat{family-given:init}{%
  \usebibmacro{name:family-given}
    {\namepartfamily}
    {\namepartgiveni}
    {\namepartprefix}
    {\namepartsuffix}%
  \usebibmacro{name:andothers}}
\DeclareNameAlias{default}{family-given}
\DeclareNameAlias{sortname}{default}
\DeclareNameAlias{labelname}{family-given:init}
\DeclareFieldFormat{editortype}{\mkbibparens{#1}}
\DeclareDelimFormat{editortypedelim}{\addspace}
\DeclareFieldFormat{translatortype}{\mkbibparens{#1}}
\DeclareDelimFormat{translatortypedelim}{\addspace}
\DeclareDelimFormat[bib,biblist]{innametitledelim}{\addcomma\space}
\DeclareFieldFormat*{citetitle}{#1}
\DeclareFieldFormat*{title}{#1}
\DeclareFieldFormat*{booktitle}{#1}
\DeclareFieldFormat*{journaltitle}{#1}
\newbibmacro*{organization+location}[1]{%
  \printlist{location}%
  \setunit*{\locdatedelim}%
  \printlist{organization}%
  \newunit}
\usepackage{xpatch}
\xpatchbibdriver{online}
  {\usebibmacro{organization+location+date}}
  {\usebibmacro{organization+location}}
  {}{}
\DeclareFieldFormat[online]{date}{\mkbibparens{#1}}
\DeclareFieldFormat{url}{<\url{#1}>}% oder {$\langle$\url{#1}$\rangle$} oder \textlangle/\textrangle
\DeclareFieldFormat{urldate}{\mkbibbrackets{\bibstring{urlseen}\addcolon\space#1}}
\renewbibmacro*{url+urldate}{%
  \usebibmacro{url}%
  \ifentrytype{online}
    {\setunit{\addspace}%
     \usebibmacro{date}}
    {}%
  \iffieldundef{urlyear}
    {}
    {\setunit*{\addspace}%
     \usebibmacro{urldate}}}
\renewbibmacro*{date+extradate}{%
  \printtext[parens]{%
    \printfield{usera}%
    \setunit{\printdelim{titleyeardelim}}%
    \printlabeldateextra}}
\renewbibmacro*{date}{%
  \usebibmacro{bbx:ifmergeddate}
    {}
    {\iffieldundef{year}
       {\printtext[date]{\bibstring{nodate}}}
       {\printdate}}}
\DefineBibliographyStrings{german}{
  nodate    = {{}o.\adddot \addabbrvspace J\adddot},
  andothers = {et\addabbrvspace al\adddot},
  urlseen   = {Zugriff},
}
\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
      \pernottype{set}
      \step[notfield=translator, final]
      \step[notfield=editor, final]
      \step[fieldset=author, fieldvalue={\string{o.\noexpand\,V\noexpand\adddot\string}}, final]
      \step[fieldset=sortname, fieldvalue={zzzzzzzzz}]
    }
    \map{
      \pernottype{online}
      \step[fieldset=location, fieldvalue={o.\noexpand\,O\noexpand\adddot}]
    }
  }
}
\renewbibmacro*{cite}{%
  \iffieldundef{shorthand}
    {\ifthenelse{\ifnameundef{labelname}\OR\iffieldundef{labelyear}}
       {\usebibmacro{cite:label}%
        \setunit{\printdelim{nonametitledelim}}}
       {\printnames{labelname}%
        \setunit{\printdelim{nametitledelim}}}%
     \printfield{usera}%
     \setunit{\printdelim{titleyeardelim}}%
     \usebibmacro{cite:labeldate+extradate}}
    {\usebibmacro{cite:shorthand}}}
\renewbibmacro*{postnote}{%
  \setunit{\postnotedelim}%
  \iffieldundef{postnote}
    {\printtext{o\adddot\addabbrvspace S\adddot}}
    {\printfield{postnote}}}
\begin{filecontents*}{\jobname.bib}
@online{test1Mit,
  author  = {Artur Autor},
  title   = {Internetquelle mit Datum},
  url     = {http://example.edu/~elk/bronto.pdf},
  urldate = {2018-03-26},
  date      = {2000-06-09},
  usera   = {Test Stichwort1} ,
}
@online{test1Ohne,
  author  = {Artur Autor},
  title   = {Internetquelle ohne Datum},
  url     = {http://example.edu/~elk/bronto.pdf},
  urldate = {2018-03-26},
  usera   = {Test Stichwort2},
}
@book{test2Mit,
  author    = {Artur Autor},
  title     = {Buch mit Datum},
  edition   = {1},
  usera     = {Test Stichwort3},
  publisher = {FOMVerlag},
  location  = {Essen},
  date      = {2000}
}
@book{test2Ohne,
  author    = {Artur Autor},
  title     = {Buch ohne Datum},
  edition   = {1},
  usera     = {Test Stichwort4},
  publisher = {FOMVerlag},
  location  = {Essen},
}
\end{filecontents*}
\addbibresource{\jobname.bib}
 
\begin{document}
\cite{test1Mit}
\cite{test1Ohne}
\cite{test2Mit}
\cite{test2Ohne}
\printbibliography[nottype=online]
\printbibliography[type=online,title={Internetquellen}]
\end{document} 
   
  