Whenever enchanted creature deals damage to an opponent, you may draw a card.
9/22/2011 “You” refers to the controller of Curiosity, which may be different from the controller of the enchanted creature. “An opponent” refers to an opponent of Curiosity’s controller.
9/22/2011 Any damage dealt by the enchanted creature to an opponent will cause Curiosity to trigger, not just combat damage.
9/22/2011 Curiosity doesn’t trigger if the enchanted creature deals damage to a planeswalker controlled by an opponent.
3/16/2018 You draw one card each time the enchanted creature deals damage to an opponent, no matter how much damage it deals or whether it was dealt in combat.
3/16/2018 If this Aura enchants an opponent’s creature, you won’t draw a card when that creature damages you. The creature has to deal damage to one of your opponents for the ability to trigger.