If Reflection token copy a Unit with When you play me effect, can I trigger that ability?

No. The Reflection token cannot trigger "When you play me" effects of the unit it copies. The Reflection card's own text explicitly states: "I become a copy of something when played. I don't get that card's play effects."

This is consistent with how Play Effects work (Rule 383.4.a). A "When you play me" trigger fires when the permanent with that ability is played to the board. The Reflection token enters play as a 0 [M] domainless token — the copy effect happens after it has already resolved and entered the board. Since the token was never played as the copied unit, the copied unit's Play Effect condition was never met.