If you can get them to open up, most witnesses will admit to either not believing everything, or at least not understanding. I spoke to a couple of elders who stopped by to see my mom several weeks ago. Since I had known these guys for my entire life, I was comfortable talking to them although I am disfellowshipped. I told them some of the things I had trouble with and one said "We don't understand everything." I asked how they could believe in something they don't understand. They didn't have a coherent response.
Before his death, I was having a similar discussion with my dad. He said he didn't believe everything but that it was the best religion out there.
The problem is, most witnesses won't open up about their real beliefs. There are a set of answers to questions for outsiders, and there's the real answers that Witnesses can give to each other. Like: Do you have to be a Witness to survive Armageddon? Most witnesses will answer to a non-witness that it's up to Jehovah. Between themselves, they claim that you have to be a witness to survive.