Usage of package `fancyhdr' together(scrreprt) with a KOMA-Script class is not recommended.
\documentclass[10pt,a4paper,titlepage,parskip=half-, listof=totoc]{scrreprt}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage[T1]{fontenc}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{color}
\usepackage{geometry}
\usepackage{graphicx}
\setkomafont{captionlabel}{\normalsize\bfseries} %Abbildung wird fett, der Rest nicht
\geometry{a4paper, top=20mm, left=28mm, right=35mm, bottom=25mm,headsep=10mm, footskip=12mm}
\makeatletter
\renewcommand*\l@figure{\@dottedtocline{1}{0em}{2.8em}}
\renewcommand*\l@table{\@dottedtocline{1}{0em}{2.3em}}
\makeatother
\usepackage{fancyhdr}
\pagestyle{fancy}
% Kopfzeile
\rhead{\slshape \thesection}
\chead{}
\lhead{\slshape \leftmark}
% Fußzeile
\lfoot{}
\cfoot{\thepage}
\rfoot{}
% Striche
\renewcommand{\headrulewidth}{0.2pt}
\renewcommand{\footrulewidth}{0pt}
Kann mir jemand helfen?

