Write out referenced chapter number

Use cleveref together with fmtcount:

\documentclass{scrreprt}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage[T1]{fontenc}
\usepackage{csquotes}
\usepackage{fmtcount}
\usepackage{hyperref}
\usepackage{cleveref}

\crefformat{chapter}{\chaptername~#2\numberstringnum{#1}#3}

\begin{document}

\chapter{Referenzieren}
\label{cha:referencing}

Dies ist ein Verweis auf \cref{cha:referencing}.

\end{document}

Blame Google if the German is bad.

If you want that also “Kapitel” is in the hyperlink, change the \crefformat line into

\crefformat{chapter}{#2\chaptername~\numberstringnum{#1}#3}

and if you want the number name to begin with a capital letter, use \Numberstringnum.

Yes, this is possible, but it's necessary to extract the chapter number first before it can be used. \ref... does not provide a number at all, so refcount and its getrefnumber comes into action. This will produce 1 here.

To get a verbal expression of 1 as Eins here, use \Numberstringnum or \numberstringnum for eins from fmtcount package.

\documentclass{scrreprt}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage[T1]{fontenc}
\usepackage{csquotes}
\usepackage{refcount}
\usepackage{fmtcount}
\usepackage{hyperref}

\begin{document}

\chapter{Hallo Welt}
I'm referencing Chapter~\Numberstringnum{\getrefnumber{cha:referencing}},~\enquote{\nameref{cha:referencing}}

\chapter{Referencing}
\label{cha:referencing}


\end{document}