The kids' new love is Knock Knock jokes, but they don't exactly "get" them yet... meaning that any answer can crack them up really. So, a knock knock joke book for older kids isn't that engaging.
However, this lift-the-flap book — Knock, Knock! Who's There? My First Book of Knock-Knock Jokes by Tad Hills (of the Duck and Goose series books) is perfect. It cracks them up, and each joke is a two-page spread with a flap to lift to reveal the punch line. It was an instant favorite. We already own it, it's that good. And, Erik sleeps with it under his pillow.
"Look out below!"
"Yikes!" (as a duck comes flying out of the sky...)