You can't get the current user data without their uid. If you have access to the express req object you can grab it with req.uid or if it is a socket call then its socket.uid. The value of uid is 0 if the user is not logged in.

Created a small plugin, to have access to all groups - https://community.nodebb.org/topic/4591/nodebb-plugin-ns-api-ns-api-extended