I am not sure if the average German knew it but have read that the German higher ups pretty much knew they would lose by late 1942.
once they failed to get to Moscow once winter began in 1941 they new it was over...
Most of the Generals knew it was over when America declared war on Germany.
So did the Japs. What I would like to know is what they thought of us, the US. Why fight a loosing cause for 3 more years?
I would imagine the reports coming from Stalingrad early in ‘43 did not inspire confidence in the German youth.