Socstu,
Yes, I have had some success with the question approach involving various topics.
You have to know what you are doing. Some people who have tried to get through to JWs end up getting sucked in or sucked back in!
You don't always know if you've been successful, especially if you only get one opportunity to talk with them, such as a one-time encounter at the door. Even if your question made a terrific impact, JWs are masters at keeping a poker face, especially when there is a witnessing partner with them.
I once had a JW come back alone in order to continue the discussion because what I had asked him really bothered him. He eventually left the organization. That's rare, but it does happen.
The attitude you display when asking questions is critical. If you come across as a know-it-all who is trying to "stump the JW" or humiliate them, they will label you as a "mocker," "apostate," "opposer of the truth," etc. and simply kick the dust off their feet as they walk away.
For example, DON'T use the tone, "How in the world can you possibly believe (whatever it is)?" That's an attack. It will backfire.
Your best chance comes if you show that you are sincerely puzzled or confused, troubled, perplexed, stumbled, etc. (whatever verbs you find most effective), over the issue that you are raising... that this is an issue that really is a stumbling block to you accepting or remaining in the WT religion.
Again, make sure you are well prepared and know what the WT teaching and witnessing approach is or you may find yourself getting sucked in. Also, JWs are skilled at changing the subject and getting back to their prepared presentation. Make sure you know how that works so you can avoid falling into the trap. Also, make sure you ask questions that they haven't been trained to answer. For example, don't ask them why they don't believe in the Trinity. They will happily reply to a question like that with a totally programmed response and do no thinking at all.
Make sure they address your question. Don't let them turn the tables on you by getting you to start answering THEIR questions.
After you have raised an effective question, one good diagnostic follow-up question is, "Do you see why this troubles me?" Many hardened JWs will say, "No" or "Not really..." Then you can elaborate. "Well, for me it's a trust issue. No disrespect intended toward the leaders of the WT, but before I dedicate my life to a religion or pin my eternal hopes on someone's claim to speak for God, I would need to be sure... I personally couldn't do that unless... (and then get back to your question)"
That doesn't come across as an attack. That comes across as one person genuinely trying to connect with another person regarding legitimate questions about the claims being made by WT leaders.
It doesn't always work, of course. Some -- maybe most -- JWs are just interested in making a "sale." When they realize you aren't going to "buy", they will leave.
But sometimes you CAN get past the programmed WT mindset and reach the real human being underneath.