This is my current status. I have tried a lot of things to achieve the layout in the second picture but it simply doesn't work.
Here is my code
\begin{longtable}{|p{.37\textwidth}|p{.01\textwidth}|p{.01\textwidth}|p{.01\textwidth}|p{.01\textwidth}|p{.01\textwidth}|p{.01\textwidth}|p{.36\textwidth}|}
\hline
\textbf{Conversion}
&\textbf{\rotatebox{90}{sehr deutlich}}
&\textbf{\rotatebox{90}{deutlich}} \vspace{0.7em}\raggedright{ausreichend}
&\textbf{\rotatebox{90}{weitgehend}}
&\textbf{\rotatebox{90}{gering}}
&\textbf{\rotatebox{90}{sehr gering}}
&\textbf{\rotatebox{90}{Aussage nicht möglich}}
&\centering{Bemerkungen}
\end{longtable}
\vspace{-2em}
\begin{longtable}{|>{\centering\arraybacksclash}p{.95\textwidth}|}
\hline
\rowcolor{light-gray}
\textbf{slten} \\
\end{longtable}
\vspace{-1.1em}
\begin{tabular}{@{}|p{.37\textwidth}|c|c|c|c|c|c|p{.345\textwidth}|}\hline
\multirow {brachte durchdachte, themenbezogene Beiträge ein.} & 1& 1& 1& 1& 1& 1 & {Foo mahe fsdaflkdsaflknasdflknsaaflkdsaflknasdflknsaaflkdsaflknasdflknsaaflkdsaflknasdflknsaaflkdsaflknasd aflkdsaflknasdflknsa aflkdsaflknasdflknsa aflkdsaflknasdflknsaflknsaaflkdsaflknasdflknsadlkfnsanf asdnlk nflak} \\\cline{1-7}
{beobachtete genau.} & 1 & 1 & 1 & 1 & 1 & 1 & \\ \cline{1-7}
{erklärte Sachinhalte treffend.} & 1 & 1 & 1 & 1 & 1 & 1 & \\ \cline{1-7}
{stellte Zusammenhänge zwischen Sachinhalten her.} & 1 & 1 & 1 & 1 & 1 & 1 & \\ \cline{1-7}
\end{tabular}
I really appreciate every help. I have put red pointers on what I cannot do.