Speaking of Jon being a Targ, have we ever seen how he does with fire? Would be kind of cool for people to question his parentage only for it to be revealed because he was immune to fire like Dany. But can't remember if I've ever seen him burn.
Otherwise, I wonder how they will prove he's a Targ. The records show that Rhaegar had his marriage annulled and presumably will show he married Lyanna but who is still alive that can't vouch for Jon being their son with enough credibility for everyone to believe them? Although I suppose all that matters is that Dany believe him.