Go for the foundations Gal. Ask him
1. Who told you that the governing body (GB) of Jehovah's Witnesses is the Faithful and Discrete Slave (FDS)?
Ans: the governing body.
2. When was the original GB appointed?
Ans: spring of 1919
Who told you that? Ans: GB
3. What were the names of the original faithful slave ? (He won't know)
4. On what bases were they chosen? (He will say they were humble honest seekers and spoke the truth.)
How do you know they were humble and honest seekers if you don't even know their names?
Did these men know they were appointed?
Ans: No...because they were teaching in 1919 that Russell was the F&DS.
5. Do you know what other falsehoods these men were teaching in 1919?
Ans: Jesus' 2nd advent occurred in 1874. Pyramidology, blood transfusions were ok, Christ was to be worshipped, military service ok, Armageddon would be over in 1925 and you could call Jerusalem to speak with Abraham, Issac and Jacob in 1926 and ask to have Grandma raised etc.
6. If these nameless men were appointed in 1919 and given exclusive ability to interpret scripture, you would think their interpretation of biblical prophecy would be spot on. Yet not one of their interpretations was correct. 100% wrong back then and now.
7. How did this original appointment, unknown to the appointees, pass on to subsequent GB members? Was it like apostolic succession?
8. Why do you think Jehovah waited till 2012 to reveal who the original appointees were?
9. And why did these appointees with exclusive right and ability to interpret scripture for mankind make unnecessary dangerous man-made commands that put Witnesses at serious risk? I.e. outlawing vaccinations, organ transplants, blood-clotting fractions etc...all permitted today.
10. Is 1919 a biblical date?
Ans: No.
How then do you know anything significant happened in 1919?
Ans: Because the bumblers in New York told us and if we don't believe them and their invented dates we will be destroyed at Armageddon.