I don't quite understand why \tableofcontents in a \twocolumn document yields only one column (or how to change that - ideally without including multicol just for the ToC...)?
\documentclass[twocolumn]{scrbook} % twocolumn set document-wide...
\usepackage{lipsum}
\begin{document}
\tableofcontents % ...but not working for the ToC?
\chapter{Foo}
\lipsum[1]
\section{Bar}
\lipsum[2]
\subsection{Baz}
\lipsum[3]
\section{FooBarBaz}
\lipsum[4]
\end{document}