It depends on well he is aware of himself. If he's still deeply closeted even to his own appraisal, and if he is deeply self-loathing, any mention of his being gay can put him into a panic and think you are totally out to get him for some reason.
If his state is not obvious, you might mention you have a friend, and how they are gay, and how you think it's ok and still like them. His response will define where to go next. But your foray needs to be low key and circumspect, no drama, nothing highlighting it as a Big Deal.
Perhaps in a decade or so you'll both be able to look back on it and laugh about how careful everyone had to be.
Don't be surprised if at some point he says he's gay, then jumps to "I am so NOT gay", back and forth, as part of his process. It would be helpful if he knew there were other gay Christians, other gay ex-JWs - that he can choose to accept his orientation without tossing belief in God (that might be important), or that there is life after JW.
Maybe do a little research about gay-friendly churches in the area, or some Websites that talk about "What does the Bible really say about hmosexuality?" - which is the title of a great little paperback, available from Amazon.
I think a key is to find resources for him (should he come out to you) that being gay does not make him the opposite of what he used to be - there's a big world out there full of all kinds of gay people, and being gay is just a tiny part of his humanity. It just sometimes seems huge.
Hope this helps! - VE (of the gay-but-it's-no-big-deal ex-jw class)
