What is it you are trying to accomplish? First and foremost do NOT tell him he is wrong. But if he is your BFF and you are hoping that he'll see the "truth" for what it really is then you have a hell of a project on your hands. You have already shown him that you have serious "doubts" and you don't go to meetings anymore. At this point.....anything you say that is even remotely negative will be viewed by him as an attack on his faith. If you are trying to save him from this wretched organization then you need to keep the communication line open for quite a long time. Ask him questions. Let him witness to you and agree with him. When he no longer feels like you are a threat to his "spirituality", ask him some thought provoking questions. Or say something like "you're right....understanding who the king of the north is or what the true meaning of a generation doesn't matter in the long run. What matters is that it is God's organization. What you've said to me has made a lot of sense. I don't want to live my life in limbo anymore. I told my wife yesterday that I am going to do the research necessary to prove to me and to her that Jesus selected the Witnesses in 1919 as his faithful slave." And as you do your "research" you can bring up points to mention to him that just don't add up and ask him if he can help you understand it any better. If there are enough questions that he can't answer....perhaps he'll start to wonder too.
Then again......taking this approach.....you risk him seeing through it and alerting your elders that you have serious doubts. Do you have other family and friends in the organization that you would lose if you were DFd?
Finally, if your friend is nothing more than an acquaintance. I'd do just like everyone says. I'd shut up and walk away.
Just my dos pesos
Only CONSIDER what I suggested above if he is your blood brother and you simply cannot bear to see him throw his life away.