Someone found this site by searching for:
“tom angleberger dwight knuckle-popping.”
In case you haven’t read the book yet, fake knuckle-popping is one of Dwight’s special abilities — along with origami, bad Yoda impressions and sitting in holes.
Anyway, I’m afraid the searcher must have left disappointed because I didn’t have the instructions up.
WAIT! Come back! Here they are as drawn by Kellen…