At the time of the film's production, SS-Oberführer Dr Gerhard Klopfer was the only living attendee of the Wannsee Conference. He died on January 29, 1987 at the age of 81.
Most of the conversations at the beginning of the film, in particular the small talk between offices, the dialogue between the SS and the secretaries, and the emergency phone call regarding a transport of Jews in the east, is entirely dramatic license. The actual minutes for the conference begin after Heydrich convened the meeting - exactly what the Nazi officers were doing before Heydrich arrived is not historically known and is dependent on second hand testimony and speculation.
The film takes place on January 20, 1942.
In the movie Reinhard Heydrich is advising a member of the conference to read Hitler's "Mein Kampf", page 772. The chapter on this particular page is titled "The missed revenge with the Marxism". In it Hitler described that if the German working people had only Marxists in 1914, the war would have been over after 3 weeks and Germany would have been down. In this chapter he also called the Jews "hebrew folk spoilers" and said that more German people would have been saved if they would have been "under poison gas", which is describing what was executed during the Holocaust.