PHP function fsockopen is not available. Maybe your hosting provider disabled it for some reason?
It is absolutly no problem to use DokuWiki without an internet connection. It is a bit more work to update plugins and the core of the wiki, because the updater doesn‘t work, but this is the only real constraint which I found. I‘m using a DokuWiki without an internet connection since 2014.
One other minor niggle when not connected: help pages are not available. You'll probably end up collecting a bunch of them from the main site and installing them elsewhere. You do at least get the basic syntax page included automatically.