In what book or chapter of The Twilight Saga do we learn that Edward Cullen's full name is Edward Anthony Masen Cullen?

well.... you learn Edward's full name in the book New Moon on page 39, and you only learn the Mason part, and you learn the Anthony part when the author is on a interview, and then she spills the beans, well you know what i mean *edited* well not really Anthony was in New Moon too and Mason was in Twilight too if u read the whole book huh? i must of missed that part

Yes, Carlisle said that Edward's full name was Edward Anthony Masen when he was human in New Moon when Bella had just hurt her arm.