If I use Drapion VSTAR's "Hazard Star" VSTAR Ability to poison my opponent's Pokemon with 3 damage counters during Pokemon Checkup, and I have Radiant Hisuian Sneasler with the "Poison Peak" Ability in play, does my opponent put 3 or 5 damage counters on their poisoned Pokemon during checkup?

Five damage counters. Poison Peak adds 2 damage counters to whatever the current number of damage counters are being placed for poison.

Relevant cards

SWSH11_119

SWSH11_123