The Gaffer

Legendary Creature — Halfling Peasant

At the beginning of each end step, if you gained 3 or more life this turn, draw a card.

You draw just one card, no matter how much life you've gained past 3 life.
The Gaffer's ability looks at how much life you've gained in the turn, even if it wasn't on the battlefield when you gained life. It doesn't care if you also lost life, even if you lost more life than you gained.
If you haven't gained 3 or more life by the time an end step begins, The Gaffer's ability won't trigger at all.