Wobble said: Ask your friend to show you ONE unique and different teaching that they were promulgating in 1919, that they still hold to today,that would have persuaded Jesus,( who is not just a supporter of truth, but is THE Truth), to choose Rutherford's Bible Students .
This is the key. Don't expect, or even try, to convince your friend in one conversation. Put him to research in the WT publications. Act as if YOU WANT to know the answer to this question as an interested person. Send him off to do the research and tell him you'll do some digging on your own. Make plans for a return visit (lol) to get with him and share what you both found.
Even on this second discussion, do not expect him to give in. You will have shaken up the cobwebs and got him thinking, though. These things take YEARS for many people. Some fast track to be out in a few months, but that's more rare, IMO.
I still remember back in the early 90s when I was so annoyed with the borg for outright lying to the congregations about their motives for no longer charging money for literature. It was really 100% about NOT PAYING TAXES but they told the rank and file it was a loving provision from Jehovah to spread the good news to the poor more effectively or some other BS. Almost 20 years ago I first realized something wasn't right, but it took time for the seed to germinate and grow. It took a lot of looking back to wake me up about 1975 being a WT scam (even though my family lived through it as JWs).
Point being, I'm still not quite out, but mentally I am, finally, after decades of increasing doubt and finally intensified investigation over the past year. So be patient with your friend. Do the research project and have him do it as well. Take your time. And feign interest sometimes so that he doesn't become afraid of you.