Special moves are found under their own section in the character command lists. They usually involve a directional input paired with one of the punch or kick buttons. An example of this would be Ryu's Hadouken, which is executed by doing a quarter circle towards the opponent and a punch. It's worth noting that you must CONNECT with these moves as the trophy said, blocked and evaded Special Moves don't count.
This one should come with the rest of the grinds, especially if you use Yoshimitsu's super (Windmill Blade, Half circle away from the opponent + Punch) to build the meter regularly. Local versus against a second controller or an AI opponent works well, naturally set the rounds to 4 and the health to 100% in order to reduce loading times.