Using a Gift normally takes an action. From pg 232:
Using a Gift, “accidentally” stabbing a challenger in the gut with
your klaive, hiding while watching two of your packmates breaking the
Litany, chasing a rival pack across the roof- tops — these are
If it's an unrolled action like Hands Full of Thunder, you still need to give it at least one die in order to take multiple actions (page 233). Decide whether you want to activate it first or second, and then assign it a single die from the other action's dice pool. For instance, if you have a 7-die Dex+Firearms pool and use Hands Full of Thunder, you should activate the Gift first (spend a die, don't roll it) and then roll the attack (the other 6 dice).
If the Gift in question specifically says that it doesn't take an action to use, you can just skip splitting your dice pool. If it needs a dice roll, split your dice from the smaller pool as per usual. If it's not an action and it needs a dice pool, you get the full dice pool because you're not taking multiple actions.
Spending Rage can also give you an extra (full dice pool, non-splittable) action that you can use alongside your split actions, but you can't use Rage and Gnosis in the same turn so this isn't always helpful.