Was most of the German populace aware of Jewish extermination in concentration camps during the Holocaust?

Yes. There were lots of tasteless jokes ciruclating in Germany in World War 2 to the effect that the standard (government issue) soap was made from the fat of Jews.

Answer #2Honestly nobody can really tell you for sure how much a German knew about what was going on in concentration camps... even regime opponents told later on the concentration camps were proclaimed to be correction camps for dangerous criminals... and who really knows if they really believed in rumours? But it's of course true that some people must have seen something, heard something, knew something... as there are people who delivered family, friends, neighbours, etc. to the secret state police and nowadays pretend knowing nothing...

It's just not that simple that in case you meet an elder German person telling you he/she didn't know about it, you could point the finger at him/her and call him/her a liar... it's just too complicated. I hardly believe someone never heard of it... but nobody can tell for 100%... maybe the rumours seemed too exagerated... look at today's world and how much it takes to believe some facts...