I think my approach to this would be to have a short series of questions ready that they can answer.
These questions be yes or no answered and lead to a quick conclusion if the witnesses were under mind control.
Question 1 example; I notice you enjoy studying the Bible with people and it looks like you have a lot of magazines and books to help you study. Does all your Bible training come from one publisher or source when studying the scriptures or can you investigate theology by other sources on your own.
Something along those lines. This first question is leading into the BITE model of mind control. Information control. A series of 4 or 5 questions could be asked along these lines. In the end you could tell them they are under mind control much like Scientologists and that they need to seek help from a psychologist. I would use tact however and word it properly without being offensive.
I also have preached quite effectively to Jehovah's witnesses about Church history. Knowing they have no history to stand on.
Question example; Imagine the year is 1850, which was not too long ago, and the day is Sunday, and you wanted to serve God and worship him. You want to study the Bible and learn about God. Where would you go to do this? What church would you attend?
This question leads them to understand that God would not abandon people in any age to spiritual darkness. Use support from Mathew 16:18
And finally another way I use to get them to think is to show them the faults of Sola Scriptura, or the Bible alone mentality that the protestants have. I personally am not protestant. Therefore I use a reasoning to show them their interpretations can be wrong. Their reasoning book does not give them much support in this area.
Comment and Question example: I don't believe the Jehovah's witnesses watchtower publishing company interprets the Scriptures correctly. Everyone that uses the Bible has their own interpretation wouldn't you agree? And wouldn't you agree that their are thousands of different religions, with new ones added each day? Everyone has a different view of the Bible. Why do you believe you have the correct interpretation of Scripture?
This kind of question leads me to show Scriptures in the Bible about tradition such as 2 Thess 2:15 as well as the council of Jerusalem decision in Acts to show that the "Church" is a composite of these three in which the Holy Spirit was guiding all along. However if your not Catholic or Orthodox you may want to avoid this approach because it sets up the conversation toward that end.
Finally,
I usually tell them that I believe C. T. Russell started the Watchtower corporation and began the Bible student movement. They agree. I then ask in such a way that will put them in an ackward position to support Russell as being a person able to interpret Scriptures on his own.
Possible Question; Can a person study the Bible alone and come to a correct understanding? Wait for answer. Why was C.T. Russell able to come to a supposed correct understanding of Scripture when millions of people through the ages before were not able? Can you prove Russell was a Holy man much like the apostles and that the Holy Spirit guided him.
This approach can set up the scenario in which you claim that Jehovahs Witnesses theology and corporation developed from a man in recent history. Another question based on the idea that their interpretations are wrong would be.
How do you know that your religion is not been corrupted by false interpretation from a man like Russell who studied the Bible alone?.
Anyway that is how I usually approach things from these three angles. More questions can be added as the situation develops.
Another question I just thought of that I asked some witnesses one day was; How do you know your not in a false religion?
I look forward to learning some other ways too.
Peace
Maksym
