The first thing you have to do after installing the Plugin is to configure your DokuWiki installation. Go to settings->DW2WP. There you have to configure the base adress of your DokuWiki installation (e.g. https://studiwiki.tu-dortmund.de).
After that you may include a DokuWiki page into a static page using
<dokuwiki>/ns/pagename</dokuwiki>
You might try this using the DokuWiki installation at https://studiwiki.tu-dortmund.de and the command
<dokuwiki>/gremienstudis/stupa</dokuwiki>
Your DokuWiki might be set up so that the ns separator uses : instead of a / (e.g. https://yoursite.com/ns:site). I don’t know if the plugin is working with the : separator (if it does, please report it to me!).
In the end you should provide some CSS under settings->DW2Wp. Use HTML before and HTML after to provide a div with an id so that you can configure the CSS.
I hope it’ll work now!