I know what you said is right, it is so frustrating that he can say one thing and the very next say another! One minute it's yes, ok, I can look into this or that, the next is 'can't do, the idea came from apostates'.
Here is a simple way around this thinking.
1.Ask the JW if the definition of TRUTH is: that which fully and completely matches reality
2.Is TRUTH simply what an authority figure tell you is true?
In other words, is there a way a person today can act which honestly allows THE TRUTH to be seen as matching/not matching reality?
Think about telling them this:
Jesus was a Jew. Who did he debate with about TRUTH in his religion?
Answer: members of his own religion!
Think about it: Jesus avoided discussing doctrine with non-Jews!
Did this make him a Jewish APOSTATE just because he debated the meaning of scriptures?
Because doctrines, beliefs, rituals and traditions can make the word of God invalid if the meaning is lost.
Jesus wanted clarity of understanding and not mere observance of Authority.
The JEWISH RELIGION had become nothing more than empty ritual observances handed down by AUTHORITY.
Jesus set the example which Christians say they are supposed to follow:
ASK THE QUESTION OF YOUR OWN RELIGIOUS AUTHORITIES: IS WHAT YOU ARE TELLING US really TRUE?
There would be no Christianity had Jesus simply accepted everything handed to him by Rabbinical teachers.
We cannot call ourselves Christian if we do not engage in the same kind of discussion with authority in our own religion which Jesus did.
Because those in Authority (Faithful and Discreet Slave) are given more by Jehovah and more is demanded of them in return.
Who is the Unfaithful Slave? The one who beats the servants and treats them badly.
How? By making them do things simply because they are TOLD TO DO THEM.
That is why the question is asked?
"Who then IS the faithful and discreet slave?"