You can find the answer on page 165 of the Beast: the Primordial core book. That's where you can find the rules both for Grappling and for Touching an Opponent. One does have to make a Dexterity + Brawl roll to deliver an attack via touch. (It mentions Fist of Nightmares explicitly, but there doesn't seem to be a reason to make exceptions here.) If you're in a grapple and succeed, you'll be able to Break Free or Hold your opponent to make that attack more easily delivered.
After that, you'll make the opposed Satiety + Manipulation roll versus the
Beast’s Satiety + Lair that "Your Power Is Mine" requires.
It seems needful to also mention that Insatiables are not a PC splat; they're an adversary from the Night Horrors: Conquering Heroes book. If you're acting on the Insatiable's behalf, you might decide that your NPC can deliver the attack through skin contact alone. But if you want to follow the rules, there they are.