Does a creature with deathtouch and lifelink gain you life when it deals combat damage to a planeswalker?

Lifelink is a static ability that causes damage dealt by the creature to also cause its controller to gain that much life (CR 702.15b). This applies to all damage the creature deals — to creatures, players, and planeswalkers alike.

When a creature with lifelink deals combat damage to a planeswalker, the damage removes loyalty counters from the planeswalker (CR 306.7) and simultaneously, because of lifelink, you gain life equal to the damage dealt. The two effects happen together as part of the same damage event.

Deathtouch (CR 702.2) is also relevant here, but only if the creature were blocking or being blocked by another creature — deathtouch causes any amount of damage the creature deals to a creature to be lethal. It has no additional interaction with the planeswalker damage or the lifelink life gain; those work independently.

Example: You attack your opponent's Liliana, Dreadhorde General (5 loyalty) with a 3/3 creature with deathtouch and lifelink. It deals 3 combat damage to Liliana, removing 3 loyalty counters, and you gain 3 life from lifelink. Deathtouch does nothing here since no creature was damaged.

So yes — any time a lifelink creature deals damage, regardless of the target, its controller gains that much life (CR 702.15b, 510.1).