I was able to find and extract my data using the shared folder function. It looks like everything went well, although i did not test the Keepass-Database yet but it seems my Whonix-related problems are solved for now.
Here is how i could find and copy my data, if it is of any use to anyone
I setup the Shared Folder as described in here
After that, i got into the Console in my Workstation and used
find . -iname new\* to search for the Document i wanted to find, because i knew the name was something like NewDatabase, and there it was, NewDatabase.kdbx, the file i searched for.
Next i used readlink -f NewDatabase.kdbx to get the full path of the Document, which was /home/user/Documents/NewDatabase.kdbx
Having found the full path of my Database, and knowing there were a couple of other Documents in the Folder i decided to copy the whole Folder Documents into the Shared Folder using
sudo cp -R /home/user/Documents /mnt/shared
Now what's left to do is to setup a new Whonix-Workstation, which i definitely will do tomorrow, and hoping i don't get into such a situation again...
Anyway, thank you @Patrick, @entr0py for your big help, as a newbie I learned a lot, really appreciate it.
Have a nice Day