Re: WWI military service for Austrians living in Germany #germany
I think 3. and 4. are both possible, but 4 is more probable. I know that even Germans and Austrians who lived in the United States or South America were called in the German or Austrian Army.
5. If he was in the Austro-Hungarian Army, you would find his records in the Austrian State Archive.
If he was in German army you need to know in which German Army he was. The service records for the Prussian Army don't exist anymore.
But the service records for the Bavarian Army are online on ancestry, the ones of the Army of Baden and the Army of Württemberg are also online.
The first step should be to search the person of interest in the Verlustlisten of both the German Army and the Austro-Hungarian Army.
If you find him in this lists you will see which army, regiment and company he was attached to.
In the Verlustlisten you can find not only soldiers who died in the war, but also wounded, missing and captured soldiers.
The Austrians have Verlustlisten and "Nachrichten über Verwundete und Kranke" = "Notices about wounded and sick soldiers".
Verlustlisten of the German Army
Verlustlisten of the Austro-Hungarian Army
Anno has both the Verlustlisten and the "Nachrichten über Verwundete und Kranke" = "Notices about wounded and sick soldiers".
Unfortunately I didn't find any Knisbacher neither in the Verlustlisten of the Germany Army nor in the ones of the Austro-Hungarian Army.