That is the million dollar question isn't it.
I think the bottom line is whether or not that the person NEEDS to believe in the jw.
The way to find this out is ask:
"If it wasn't the truth would you want to know?" or
"Pretend I have a peice of paper here, and it has irrefutable evidence that the jw aren't God's organization. Do want to look at it?"
If the answer is NO, then it is not truth they love (because the way truth is best understood is by a constant search for facts and ideas and modifying OUR concept of truth according to those), but rather "the truth" (this requires only looking at facts and ideas that support "the truth" and refusing to acknowledge or look at facts or ideas that refute it).
If that is the case then they NEED to believe in the jw. I don't think there is any point in showing them anything. You have to first identify, then create conditions that remove the need.
If they don't NEED to believe in the jw (unlikely) then your task is simplified. I heard someone here say that "the door you came in through is the door you have to leave through". What that means is don't take them stuff YOU think is important. Rather find out what the hooks were for them. Remove the hooks through humble and presentation of facts and ideas and asking them to square these with their beliefs..