The classic knock knock joke has so many hilarious variations, and they're all here.

Knock, Knock

Who’s there?

Worm!

Worm who?

Worm to meet you!
Knock, Knock

Who’s there?

Can!

Can who?

Can I worm my way in to your house!
Who’s there?

Can!

Can who?

Can Of Worms!
Knock, Knock

Who’s there?

Glow!

Glow who?

Glow worm!
Knock Knock
Who's there?
Mary
Mary who?
Mary Christmas!
Knock Knock
Who's there?
Holly
Holly who?
Holly-days are here again!
Knock Knock
Who's there?
Anna!
Anna who?
Anna partridge in a pear tree.
Knock Knock
Who's there?
Oakham
Oakham who?
Oakham all ye faithfull!
Knock Knock
Who's there?
Wayne
Wayne who?
Wayne in a manger!
Knock Knock
Who's there?
Snow
Snow who?
Snow business like show business!
Knock Knock
Who's there?
Centipede.
Centipede who?
Centipede on the Christmas tree.
Knock Knock!
Who's there?
Rabbit.
Rabbit who?
Rabbit up carefully, it's a present!
Knock Knock
Who's there?
Donut
Donut who?
Donut open til Christmas!
Knock Knock
Who's there?
Two 4's.
Two 4's who?
No need to make lunch we already 8.
Knock Knock
Who's there
Four Eggs
Four Eggs who
Four Eggs ample!
Knock Knock
Who's there?
Water!
Water who?
Water way to answer the door!
Knock Knock.
Who's there?
Pasta!
Pasta who?
Italian chef who pasta away.
Knock Knock Who's there?
Pecan!
Pecan who?
Pecan somebody your own size!
Knock Knock
Who's there?
Greece!
Greece who?
Are Greece and oil the same thing?
Knock Knock
Who's there?
Ireland!
Ireland who?
Ireland you money, if you promise to pay me back.
Knock Knock
Who's there?
Irish!
Irish who?
Irish you a happy St. Patrick's Day!
Knock Knock
Who's there?
Rome!
Rome who?
Rome is where the heart is!
Knock Knock
Who's there?
Italy!
Italy who?
Italy all over in the morning.
Knock knock
Who's there?
To.
To who?
Surely you mean to whom.
Knock Knock
Who's there?
Spain!
Spain who?
Spain to have to keep knocking on this door!
Knock, knock.
Who’s there?
I am.
I am who?
You mean you don’t know who you are?
Knock, knock.
Who’s there?
Hoo.
Hoo who?
Are you an owl?
Knock, knock.
Who’s there?
Two knee.
Two knee who?
Two-knee fish!
Knock, knock
Who’s there?
Ben.
Ben who?
Ben knocking For 10 minutes.
Knock, knock.
Who’s there?
Police.
Police who?
Police hurry up, it’s chilly outside!