I agree with Black Sheep.
You can't teach a JW anything because they're sure they have the truth and you don't.
Use questions instead.
The monkey is on their backs to come up with answers to prove they've got the truth.
Of course, they won't be able to do it, but let them try.
Make sure the questions aren't stated sarcastically (a real temptation, I know).
I've found that a good diagnostic question is, "Do you see why this puzzles (bothers, troubles, etc.) me?"
Usually they'll say "no" because they don't want to concede anything, but not always."
I once had a dub say, "Yes, I don't agree with you but I can see how you might think that."
His partner stared a hole through him.
The one who admitted he saw where I was coming from eventually came out.
He told me later, "I didn't agree with you at the time, but I could see the issue wasn't as one-sided as the Watchtower tried to portray it."
Even if that's all the farther you get, you've accomplished a lot merely by asking questions for which the WTS has no good answers.