Allow me to clarify. If one has possession of one of their bibles, then one can familiarize themselves with that version, and then compare that to whatever translation you wish, and ask them why does a verse says what it does. In other words, quote a verse from an authentic bible that you know is clearly altered in the NWT. When the NWT is pulled out by them and you both see that it is different from your own when you pull yours out, ask whose is right? They’ll go through all their gyrations to defend it, but in the end, they’ll lose all creditability. Why? They can’t tell you who translated it! The WTS won’t reveal the translators, although this info is know readily available on the internet.
The JW’s do not know the bible as well as some think they do. Look at some of the converts from mainline Protestanism such as Marcus Grodi or Scott Hahn, that did not know 1 Tim.3:15. These men were intensely trained at the university level, and they didn’t know this scripture! Why? Because they looked at the bible through their Calvinist glasses. Same thing with JW’s. So they do know their doctrinal teachings from their bible, but if one knows the bible even better and points to them some key verses that support the divinity of Christ, heaven for all, the Eucharist, etc. then at the very least a seed can be planted.