Knock Knock! Who's there? Harry! Harry who? Harry up and answer the door Knock Knock! Who's there? Nobel! Nobel who? No bell so i will knock Kids can't get enough of laughter so they can't get enough of Alex Addo hilarious joke books. The best selling book Knock Knock for kids will have kids and kids at heart busting a gut and asking for more Alex loves spending his spare time with his wife and kids laughing out loud to his jokes.