I don't understand how this ability is actually supposed to work.

We're not allowed to see each other's action cards, but we can trade them? Does one player just tell the Hacan what they have and sort of blindly try to trade? Can they lie? If players are allowed to show each other action cards, they aren't required to show Hacan their hands, obviously.

I'm really surprised there's not more questions here about this ability. It makes very little logistical sense to me.

Also, tangent question, if Jol'Nar play the action card that lets them use the secondary policy after triggering the primary (synchonicity, I think?) on a technology policy, do they then re-trigger the primary for a total of three techs?

I'm not aware of any rule that says players MUST keep their Action Cards secret. As a hand of cards it follows, from general board game logic, that they are kept hidden until they are used and I expect most players naturally follow that motif. However, it is a not a rule that must be obeyed. A quick scan of the Action Card section from the rulebook supports this understanding - I see no explicit rule saying they must be kept secret.

Of course, there's also no rule that says someone trading ACs with the Hacan is required to reveal the cards he's offering. In theory, the player could lie to Hacan about what cards he's giving (just as Hacan could lie about the cards HE'S giving) but frankly, if I were the Hacan player I would simply refuse to make any trade unless I was guaranteed to be getting the cards I was promised. Just because Hacan CAN trade ACs with people doesn't mean he HAS to. Conversely, if Hacan (or his trading partner) doesn't take appropriate precautions when trading, he has no one to blame but himself if he gets screwed.

The potential for deception exists, but the way to manage it within the rules is fairly straightforward, which is probably why you don't see that many questions about it. The only cards that DO have such a rule (that I'm aware of) are Secret Objectives, where it explicitly says your SO will be forfeit if you reveal it to anyone prior to having completed it.

As far as the other question goes, I'm not 100% sure, but I think that's valid. When racials and cards line up they can make very powerful combos. It won't happen every game, though, so it's not broken, it's just lucky.