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