The most glaring difference is in the deity of Christ. They say no. Our Bibles say yes. The single most clear text that says that Jesus was actually God is John 1:1.
In the beginning was the Word, and the Word was with God, and the Word was God. (John 1:1)The NWT says it slightly different.
Originally the Word was, and the Word was with God, and the Word was a god."So? Doesn't it say the same thing?" Not quite. You see, there are passages in which humans are referred to as gods (lowercase "g"). See, for instance, Psalm 82:6 and John 10:34-35. See? No "Jesus is God" required.
Now, truth be told, no reputable Greek scholar would render John 1:1 as "a god". It's not in there. It's not right. But at this point, let's leave that alone for a moment because I don't think you have to butt heads here over a meaning of a Greek word to make your point. Look a little farther down.
All things were made by Him, and without Him was not any thing made that was made. (John 1:3)Now note the NWT version.
All things came into existence through him, and apart from him not even one thing came into existence.Well, that is pretty much the same. If anything, the NWT is more emphatic. "Not even one thing." You see the problem, don't you? They say that Jesus was a created being. Oh, a high-end created being, but a creation nonetheless. So He cannot be God. God is uncreated. Jesus was, in the terms of the first translation, "made" or in the second, He "came into existence". So Jesus is absolutely unique because, as it turns out, He was able to create Himself. Before He came into existence, He caused Himself to come into existence. At least, if we're going to remain faithful to the text -- to their text -- that's the only possible conclusion. Because their text says "not even one thing came into existence" apart from Him. You see, we have a dilemma here. If Jesus is a created being, a "made" person, if He "came into existence" rather than being eternally existent as God, then He made Himself, an absolute impossibility.
We need to pray for people to meet Jesus, the Son of God, the image of the invisible God (Col 1:15), the One in whom the whole fullness of deity dwells bodily (Col 2:9). Nothing less will do. We need, then, to pray for Jehovah's Witnesses. Maybe this can give an opening for a discussion away from the tried patterns of John 1:1 and a pause long enough for the Spirit to come through. Like each of us, they need Jesus. The one they have is not the biblical Jesus.