If they are being disrespectful and look like they haven't read the book I'll be a bit more immature when asking if they did. Likewise if they respectfully state their opinion and it doesn't seem like they didn't read it I'll ask politely or simply not question it at all and just go right to the debate. I'm more of a reflect the attitude I am given person.

I guess it depends on if you're just trying to ask, or you want to accuse someone.

Totally agree with Zanhar. Besides, it's kinda obvious in most cases. Whenever I watch a Twilight, HP, or Hunger Games film with some of my friends they tend to ask a ton of easy questions (example: whats Edward's power? What's a patronus? Why are the tributes from 1, 2, and 3 so excited for the Games while everyone else is dreading them?). Basically questions that can be easily asked by reading the books. In that case I'd explain it and say "I recommend the books"

You could just answer their questions instead of telling them to invest 50 hours into reading just to answer a simple question.
If I hasn't already read them, I wouldn't waste my time, it wouldn't be worth it

If you're referring to me I said "I'd explain it" (answer their question) AND THEN recommend the books ;)

Straight out asking them is best.

@ anydayynow: sometimes how you phrase the answer of a question depends on how much knowledge of the book the other person has. Eg if they've read the books, then you can use terms used in the book without worrying about them not understanding you (muggles, horcruxes, animagi, azkaban, etc). Other answers depend on previous knowledge of a character's history that someone who hasn't read the books might need to be told first. So knowing whether they've read the books helps you to better answer their question.

@anydaynow Asking a question about the book is different than going "Harry got Hermione pregnant in book 5". If they ask a question sure I'll give them an answer rather than telling to go read (of course I'd recommend it to them because it makes debating easier for them and might help them find a new book they'd actual;y like). But if they just make ridiculous assumptions like in the example above then I'd tell them to read the books before slinging insults.

Ok? i didn't ask anyone why they would need to ask.