How do I get a parent-group alias as token for the Pathauto module? When a user sets his groups alias to lets say "mynewgroup" you can view the group at www.example.com/mynewgroup.

How to set pathauto presets to create www.example.com/mynewgroup/mynewgroupcontent as a path for a newly created group-content?

I can not find a token for parent's group alias.
I can only find [group_content:gid:entity:url] - but this provides full path and not only the alias.
Not possible at the moment (unless you make it yourself), there is an issue in the module's issue queue though that also has a patch that might work:

https://www.drupal.org/node/2774827