Whose kitchen knife was it? Who's switchblade was it? Why did Mr. Tate say that he had taken the switchbalde off a drunk earlier that evening?

The kitchen knife belonged to Boo and the switchblade belonged to Bob Ewell. Tate might have taken the switchblade as evidence but also to make it look like Bob Ewell held the primary weapon in order to protect Boo and Jem by saying that Ewell fell on his own knife.