Some Pokemon may learn it or try going to the move tutor which is in a little west from fallarbor town.
Tri attack is no longer a TM to teach that move you must find a move tutor that teaches the move in the game.
you don't
In Pokemon I've never heard of that attack Could you mean: Double Kick or Tri attack. If you mean Tri-attack the well: Tri Attack does damage, and has a 20% chance of either paralyzing, freezing or burning the target. Each ailment has a 6.67% chance of being inflicted. The Pokemon that learn it is: Duduo, Dodrio, and all the Porygons! So i think you meant Tri attack.
tri attack is not a TM in platinum. tri attack used to be a TM, and could be found on the roof of the celadon department store, but future generations replaced it.
There is no best level to evolve Magneton into Magnezone as long as it knows Tri Attack before you evolve it if you want it to know Tri Attack because Magnezone cannot learn Tri Attack in any way because other than Magneton learning Tri Attack via the Move Re-learner, their move pools are exactly the same except for a Move Tutor being able to teach Magnezone the Iron Head attack which is a move that Magneton cannot learn.
Magneton can only learn Tri Attack through the Move Relearner in Pastoria City in Pokémon Diamond, Pearl and Platinum.
dodrio (evolution of doduo) and magneton (evo of magnemite)
its not a TM but dodtrio can learn it by leveling up.
Dodiuo at level 30 should have Tri Attack. It attacks with Fire, Water and Ice
its Fairly Decent had the Attack Power of 70 but Flamethrower has 95 and Blizzard has 120 (Just for comparison)
Ice-type Pokémon cannot be frozen by Ice-type moves; however, they can be frozen by Tri Attack.
you cant