Well, it says "subject," for the first blank, so you should put in the topic, not the book title. And the second blank asks for the title. So put in the book title there.
But I doubt it matters.
The person who sent you the NDA probably didn't write it. Probably didn't even read it.
You should read the NDA, fill it out as best you can, and send it back. If there's a problem, they'll tell you. Don't worry so much about this.