What did the German people know about what was happening in the camps?
The existence of the extermination camps was also known in outline, though many Germans didn't want to know about the holocaust and took the line of 'hear no evil, hear no evil'.
So it's hard to say - the first answer gives an important idea. It's of course true that some people that had delivered their own family members or neighbours to GESTAPO (secret state police) pretended later they didn't know anything about that. But it wouldn't be correct to call a German a liar if he/she would tell you, they didn't know what happened - it's just hard to say...
As for the ordinary concentration camps, they were feared.
On the more general issue of what was known, here is what the historian Helga Grebing (born in 1930) wrote in an early, respected short history of the Nazi period:
'Protective custody, the concentration camps, the boycott of Jewish businesses, etc., emigration, persecution, the Yellow Star, the treatment of prisoners of war and slave labourers from Eastern Europe - nobody who lived in the Third Reich can claim to have known nothing, absolutely nothing, about all that'. […]
'In 1945 the mass of silent, inconspicuous fellow-travellers claimed never to have had anything to do with Nazism'.
Helga Grebing, Der Nationalsozialismus: Ursprung und Wesen, Günther Olzog Verlag, Munich, 1964 pp. 130-31. (First published in 1959).