score:5
Jehovah's Witnesses preach in over 240 lands, collectively reporting over 2 billion hours in the ministry annually. I'm sure there are many such encounters with demon-possessed individuals. However, these stories will be quite rare because (1) demon possession is generally rare, and (2) Jehovah's Witnesses don't aim to spread fear of the demons by telling such stories. The ministry is about telling the good news.
I was able to find a couple of experiences published in old Yearbooks and Watchtowers.