Knock, knock! Who's there? Spell. Spell who? W-H-O.
Peter approaches the gates of Heaven. "Knock knock," says Peter. Miraculously, someone answers him. "Who's there," a voice in the distance asked. "God," says Peter. "God who," asked the voice? "GOD DAMMIT open these gates! I've been a good neighbor, loved my wife and lost my virginity, twice!"
Knock knock Who's there? Double. Double who? W!
Knock knock! Who's there? Yah! Yah who? Naaah, bro, I prefer google.
Fast way to screw up someone's Knock Knock joke...? "It's open."
Knock, knock. Who's there? Owls say. Owls say who? Yep, that they do.
Knock, knock. Who's there? Nobel. Nobel who? No bell, I knock.
Knock knock. Who's there? Hatch. Hatch who? Bless you.
Knock Knock! Who's There? Figs Figs who? Figs the doorbell, it's broken!
Knock Knock. Who's there! Ice cream! Ice cream who? Ice cream if you don't let me in!