Knock knock. Who's there? Vaughn.

Vaughn who? Vaughn voyage! Hope your journey's ship-shape and full of bon-bons!

Knock knock. Who's there? Continue.

Continue who? Continue the joke. That's the whole thing. No pun.

Knock knock. Who's there? Olive.

Olive who? Olive your jokes are so funny!

Knock knock. Who's there? Parenthesis.