Forum:Breakthrough Skill ruling on graveyard

So, i have Skill Breakthrough on my graveyard, and my opp has a negating magic/trap (ex. Shi En). Let say it was my turn and i activate a spell, then my opp using the Shi En eff, can i still play Breakthrough Skill to negate the Shi En eff? Or do i need to activate the Breakthrough Skill first? (Which he/she might negate the trap eff).

Someone pls clear this thing for me. Thanks.