Knock knock.
Who’s there?
Not your.
Not your who?
Not your mama!
Knock knock.
Who’s there?
Not your.
Not your who?
Not your mama!
Listen up, chucklehead! This joke is a knock-knock. It relies on wordplay. The joke is that the response to "Not your who?" is "Not your mama!" It's funny because it sounds like "Not your mother!" Simple, right? I'd be surprised if you got it.