Your question doesn't make complete sense as written. "Going solo" - the first time a pilot flies a plane without an instructor aboard - is a universal part of pilot training, so any Luftwaffe airman trained as a pilot (many airmen for all combatants were non-pilots, e.g. gunners and navigators) would have flown solo at some point early in their pilot training (even if they later piloted larger planes with a co-pilot).

Here is an account from one Luftwaffe pilot's first solo flight:

Early in July 1942 our course was moved out to the school’s satellite field at Bad Wörishofen. This small station was set in picturesque countryside about fifty kilometres WSW of Fürstenfeldbruck. The buildings were all of wooden construction and there was an altogether informal and relaxed–in fact, almost civilian–air about the place. It was here on 15 July 1942, after forty-five flights with the instructor literally looking over my shoulder, that I first went solo. I lifted off in Stieglitz PF+UT at exactly 10.36hrs. One careful circuit and I brought her gently back down to earth again at 10.40hrs. Although flight number forty-six may have lasted only four minutes, it was entered into my logbook with a real sense of achievement. Another hurdle cleared in my ambition to become a fighter pilot. (Source: Wolfgang Fischer, Luftwaffe Fighter Pilot)

In combat, many (most by the end of the war) German planes were single-seat, single-engine planes, so of course any pilot of such a plane would be "flying solo".