You don't copy a move, you copy the ability;
>Upon switching in, the wielder copies the opponent's ability. In doubles and triples battles, Trace randomly selects which opponent's ability to copy. Trace cannot copy Flower Gift, Forecast, Illusion, Imposter, Multitype, Trace, and Zen Mode. If the opponent has just been KOed, Trace will copy the ability of the next Pokemon revealed in the battle. Trace will immediately activate whenever the ability is acquired, such as through Skill Swap or Role Play.
You mixed it up it seems. You gain the effect of the Opponent's ability with trace, not one of their moves - your moveset remains completely the same