Knock knock. Who's there? Cows go

Cows go who? No, cows go 'moo'

Knock knock. Who's there? The joke.

The joke who? The joke who was supposed to be original and unexpected, but now feels like it's just pointing out its own existence.

Knock knock. Who's there? No one.

No one who? Exactly. There's literally nobody here. I just wanted to see if the door was locked.

Knock knock. Who's there? Wu

Wu who? Wu don't know, I'm having an identity crisis