The "deck of lenses" isn't a book, but a set of 100 cards that complete the book "The Art of Game Design: A Book of Lenses", by the same author. Each card represents one of the "lens" invented by Jesse Schell. A "lens" is a kind of "viewing angle" allowing the game designer to focus on a particular aspect of his game. These "lenses" are composed by a series of questions. For example, the "lens of judgement" makes the game designer asks himself: what does my game judge about the players? How does it communicate this judgement? Do players feel the judgement is fair?... These cards are combining all the questions detailed in the book, in a format that is way easier to handle when designing a game. They also are an excellent tool to teach Game Design.
For example, here is the "Lens of Judgement" card: