The book has a large number of pages. It is red and has "Frown Digest" written on the cover in dark purple.
Role in episode
Squidward reads this book near the beginning of the episode. SpongeBob then starts talking about how he will win the Employee of the Month Award again. Squidward is no longer reading the book after SpongeBob is told by Mr. Krabs that Squidward could end up winning the award.
It is a reference to the fact that Squidward rarely smiles.