With all due respect to Mr. Van Gogh, I don't recommend Crisis of Conscience as a first read. It is a VERY good book if you are a JW. But I have heard other non-jw's, and from my own personal experience, that COC is kind of hard to follow if you aren't/weren't ever a dub.
First thing you need to do is keep the trust built up with your son.
Second learn about cults. Helping someone out of a cult is a process, and not simply a matter of finding information to refute his belief system. You have to understand that mind control does not allow rational thought processes to penetrate the protective wall of the cult identity.
Next, learn about the JW. I am not sure what is the best choice here for an outsider. I sure haven't read a better one then COC. But there are hundreds of pages that left me with a ? One that isn't to bad for building an argument against the WT being divinely chosen is Captives of a Concept. It has a tight line of reasoning and relies only on JW literature to make it's case. That is nice because you can literally spend years unraveling the JW web of lies. Look for what has the mosts bang for the buck and will matter most to your son. You will find that the WT has been extremely arrogant over the years, and said a great many silly things. There is a site that is dedicated to simply quoting the WT, www.reexamine.org
Some more good info sites are freeminds.org, ajwrb.org, silentlambs.org, brci.org, jwreform.org...
Go to the hall with him. He will just be ecstatic! Meet the folks at the hall. Ask them about their personal lives. Don't let them put you in a charicature. He will try to get you to start a study, try to avoid that!
That ought to keep you busy.
Spend plenty of time here asking questions. Try to enlist other family members. What is the status of her family?
And if you are a Christian, pray. Alot!
CYP