According to amazone.co.uk the messages are in the comic strips. Hope that helps. Haven't read the book myself but was intrigued!
quote "Also I liked the small in-joke that Picoult uses the way through her interjective comic book drawings. When being told how Trixies parents met, her mother explains the secret message that her father left for her in a caricature he made of her a secret message.If the reader looks closely in the pictures of the comic book they will also find hidden messages waiting for them. "