If Snowden plays his cards right, (I know this is a rigged game), all he has to do is counter-sue and ask (through his lawyer), “In what part of the book did I violate the NDA?”
If the state is going to make a claim of “national security,” then the judge could say, “OK, now I am confused, you have 15 days to articulate where the NDA was violated, while you yourself abiding by your national security claim, else it is case dismissed.”