Good question!
This is a real risky area for the WBT$, but...
Asking rather than telling is the way to open a closed mind. This can take time, patience, commitment and well thought out strategies - something few people have these days.
Probably reverse witnessing by workmates (again by means of questions) may pose a bigger danger to the WBT$.
I was asked to explain what the gospel is in one word! That simple!
Instinctively I knew I had been asked a Bible 101 question and was inexplicably ignorant of the answer. I was determined not to remain ignorant! Also one cannot continue following both the WBT$ and the gospel since they go in different directions. It did take 3½ years of intensive and exhilarating research (oddly enough in the WBT$'s own publications) until it was clear the gospel was not in their hearts and not on their lips, and we parted ways. In time it also became clear that all religion effectively is opposite to the gospel.