This is not hard for a learned JW. They can easily respond that "Israel" refers to the spiritual Israel (hence the anointed), while ''all nations'' refers to, well, all nations. Arbitrary reasoning of course, but this is the 'correct' jw answer.
Things that have to do with the Org and the GB are far more likely to awake someone to TTATT. And if he's science-inclined, evolution, naturally.
If you are allowed to use *only* the Bible, there are dozens of things: The genocide of the Canaanites is one of my favourites. After reading some passage from Joshua or Judges (involving lot of slaughter), you ask: "What would you do if you were an Israelite Jehovah's witness at the time of the conquest of Canaan? Would you take the sword and slaughter kids, infants, and women?"
If he answers ''yes'', then you ask: "How can you, then, state before the secular authorities that you are a conscientious objector, that your conscience does not allow you to even HOLD a weapon, let alone use it???"
If he answers ''no'', then you say: ''Well, that would be disobeying Jehovah's organization. Would you disobey Jehovah's organization TODAY if your conscience told you so? The Organization today teaches that the annihilation of the Canaanites was justified. Do you agree with this or not?" [if he agrees, this contradicts his previous negative answer].
I've used this exact sequence in a couple of persons, and they did get a little disoriented...