I won't give you anything to ask because I'm sure you know as much & probably much more than I do & Vandy gave you loads, too.
But one thing I will say. In my experience asking questions is by far the most powerful technique for waking people up. Making statements that clearly debunks their doctrine just shuts them down, as they're trained to do.
Socratic questioning is the key.
Of course sometimes you can couch the answers in questions, such as "I heard many early Bible students didn't become Jehovah's witnesses. Do you think it's because they were disappointed when Armageddon didn't come in 1914 as Russell predicted?"