Well here I am again. I tried a fresh installation from the beginning. But now i get this:

E: gnupg, gnupg2 and gnupg1 do not seem to be installed, but one of them is required for this operation

when I try to run wget -q “ https://maven.xwiki.org/public.gpg ” -O- | sudo apt-key add -

If I try to install it I get this error (no matter if I enter gnupg, gnupg1, gnupg2):

apt-get install gnupg2
Reading package lists… Done
Building dependency tree
Reading state information… Done
Package gnupg2 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:

E: Package ‘gnupg2’ has no installation candidate

Thanks for your help