It does not question the authenticity, the reason it will be impossible to research is because there are dozens of SS Officers with the surname Wagner, and when you only have the last name on the ring, it will be impossible to narrow down which Wagner it was to just one. The method by which the owner of a ring can be determined is by using the Dienstalterliste der SS, which lists all officers of the SS higher than rank of Untersturmfuhrer (2nd Lt. ) You can use this website which has a few editions of the Dienstalterliste.

http://www.dws-xip.pl/reich/biografie/numerD.html