Knock knock. Who's there? Candice.

Candice who? Candice door open? I'm getting board waiting!

Knock knock. Who's there? Elijah.

Elijah who? A light bulb just went off, I've got a brilliant idea for a joke!

Knock knock. Who's there? Pane

Pane who? I'm having a window of opportunity to let you in.

Knock knock. Who's there? A door.

A door who? A door has no 'who,' it's an inanimate object.