\documentclass{scrartcl}
\usepackage{amsmath}
\usepackage{hyperref}
\usepackage{zref-user}
\usepackage{zref-clever}

\begin{document}

\section{sub3 with spaces}\zlabel{sec:sub3 with spaces}

\begin{equation}
  f(x) = 42
  \label{eq:sub3 with spaces}
\end{equation}

This is \zcref{sec:sub3 with spaces}, and \zcref{eq:sub3 with spaces} is up top.
The same here, but without anything clever done to it: \zref{eq:sub3 with spaces}.

\end{document}
