Porygon2 already knows Psybeam, so teaching it Psychic would be redundant. It has twice the PP of Psychic and Porygon2 already has a decent Special Attack. 65 base power is also not terrible for ingame, although it is a bit on the weaker side. Even so, technoduck should be able to tank an extra hit if necessary. By keeping Psybeam on it and teaching Psychic to someone else, you spread out your Psychic coverage so that if one goes down, you have backup.
I would recommend evolving it to Porygon-Z, because not only is it faster and stronger, it's awesome as hell. You sacrifice some bulk, but 70/75 is still solid for in-game, and you opponents can't beat you if they're dead.
VERDICT: Psychic compatible. Install if necessary.
Togekiss is an alright choice for Psychic, although it's not terribly useful when it already has Fighting and Flying coverage. Nobody in the E4 have a Pokémon with a Psychic weakness that isn't already weak to Aura Sphere or Air Slash. Teaching Psychic to Togekiss would be kind of a waste because it has no use for the move.
If you have the TM for Flamethrower/Fire Blast, I suggest teaching it to Togekiss instead of Silver Wind. I once made the mistake of having only one Pokémon on my team with Fire moves and got curbstomped by Will's Bronzong when Houndoom was KOd. If both Infernape and Togekiss have Fire moves you can avoid my fate.
VERDICT: Psychic-intolerant. Waste of resources.
Golduck is the best candidate for Psychic of the three, methinks. It already knows Zen Headbutt, true, but Psychic would be a direct upgrade playing off of Golduck's higher SpA (and no 10% chance to miss). While the same can be said for Porygon2, I think Golduck benefits from it more because of its speed and how it's not weak to Fighting moves.
VERDICT: Psychic compatible. Prime candidate.