Rulings

• Each creature with lifelink dealing combat damage causes a separate life-gaining event. For example, if two creatures you control with lifelink deal combat damage at the same time, a "whenever you gain life" ability will trigger twice. However, if a single creature you control with lifelink deals combat damage to multiple creatures, players, and/or planeswalkers at the same time (perhaps because it has trample or was blocked by more than one creature), the ability will trigger only once.2021-04-16
• You may only pay {2} once for each life gain event.2021-04-16
• If you gain an amount of life "for each" of something, that life is gained as one event and the ability will trigger only once.2021-04-16
• An ability that triggers "whenever you gain life" triggers just once for each life-gaining event, no matter how much life you gain.2021-04-16