I understand not to take communion. I think they only do communion once per year. They do this on the anniversary of the Lord’s death which they calculate is some strange way. For example, in 2010 they had it on the Tuesday in Holy Week. Only those who have the “sign” who are going to heaven are to partake, so no one does in most Kingdom Halls. So, even though I wouldn’t receive their “communion” I don’t think they’d want me to anyway.I don’t know that the Church has an “official” position. My personal opinion is that it would not be sinful for you to attend the funeral to pay respects for your friend. Of course, you don’t partake in any sort of communion service (I don’t know whether JWs do that anyway) nor recite any creeds or prayers that contradict the Catholic faith. But simply to attend and pray for your friend would be fine.
Then you should be fine. Your friend and his family need your prayers.I don’t know about things that happen at a Jehovah’s Witness funeral. I certainly wouldn’t pray or saying anything contrary to Catholic belief.