How many Nazi knew about Hitler's Holocaust?

The high ranking Nazis for sure, they were privy to everything, some would even argue they were really making the decisions and Hitler was a figure head. The Nazis who worked in the concentration camps or in connection with them, but soldiers especially on the eastern front did not. Domestic Nazis who dealt with home affairs like education and farming probably not as well, they would know to hate the Jews but it's highly unlikely they expected Hitler to exterminate them.