"Who dat dat say who dat when I say who dat" comes from the early days of talkies. I do not remember the black comedian who did it. He probably also did this schtik in Vaudeville. The scene in the movie takes place in a haunted house.
By the time I was a kid, the routine became "Who dat dat say who dat when I say 'Who dat?'" A friend would often come back with "Who dat?' and the whole thing would recycle as often as the two people would stay amused.