I think it depends on how they relate to you now and how open or close minded they are.
My own thought is that the best way to show a JW the truth about the WTS is to have them read some of the older dogmatic literature that flatly contradicts what they say today.
Examples might be The Finished Mystery (with all the pyramidology and a 4-class rather than 2-class system) or Millions Now Living Will Never Die (on pages 89-90 confidently predicting the return of Abraham, Isaac, and Jacob in 1925) or "They will know that a prophet was among them" (about how the WTS is Jehovah's prophet) or prophecies about 1975.
If you try to push it on them, they'll probably refuse to look at it.
But if you have it lying around or on a computer screen they might look at it.
If you have originals you might leave them lying on the table.
Your screensaver might be some key pages from that stuff.
If they ask you what it's all about, you can just say, "Oh, it's a Watchtower publication I was looking at."
I wouldn't even suggest that they read it.
Leave it up to them.
If they ask you anything about it, show them some of the more egregious passages and tell them the passages puzzle you.
Leave it at that.
The goal would be to get them to start thinking for themselves.
Hope these thoughts help...