Title: The Wizards of Once: Knock Three Times, Author: Cressida Cowell
Title: World's Best (and Worst) Knock-Knock Jokes, Author: Georgia Beth
Title: Garfield's ® Knock-Knock Jokes, Author: Scott Nickel
Title: Knock Knock Jokes, Author: Ima Laffin
Title: Knock Your Socks Off: A Book of Knock-Knock Jokes, Author: Michael Dahl