Gnome is a very versatile Ancestry when it comes toPathfinder: Second Edition. Their heritages weren’t directly changed as much as others in the Remaster, but they’ve been impacted indirectly. Pathfinder has undergone a lot of changes in recent years which, in a system as complex as this one, can bring some cascading effects.
There are five heritages available to gnomes in Pathfinder: Second Edition Remaster - no addition or subtraction from the number of the original Core Rulebook - which serve very different purposes. How have these been impacted by the update to Paizo’s tabletop game, and how good are they now?

5Wellspring Gnome
The gnomes that choose sources of magic other than primal are the ones most impacted by the Pathfinder: Second Edition Remaster. Wellspring gnomes had a very distinct purpose in the original version of the tabletop: they could choose arcane, divine, or occult as their magical tradition, which would make them proficient in those spells or cantrips.
With the Remaster, Paizo removed magical tradition proficiencies and placed them all under the umbrella of spellcasting proficiency. This means that wellspring gnomes lost half of what made them unique and powerful. In this newer iteration of the tabletop game, all they do is choose another tradition, which unlocks its respective spells and cantrips. You’ll only choose them if your character really doesn’t want to use the primal tradition that is innate to gnomes.

4Chameleon Gnome
These fun little gnomes haven’t been changed in the Remastered and, frankly, haven’t really been impacted by any of the other changes. Their major issue remains the same: they’re a gimmick. Chameleon gnomes have, as their name implies, control over the colour of their bodies. They can change both hair and skin colour in two different ways: small changes that take a single-action to complete (this could be, for example, changing the colour of your hands) and dramatic alterations that take up to an hour to happen.
This ability isn’t simply for visual flavor, it brings a mechanical benefit: a 2+ circumstance bonus to stealth checks if your coloration matches that of your environment. The issue is, chameleon gnomes change their colour randomly while they sleep. You can lie down in the middle of the forest looking as green as the grass you’re sleeping on, but wake up completely purple. An hour is a long time to make dramatic changes, which means that only very specific campaign settings will allow you to use chameleon gnomes successfully.

Pathfinder Definitions:
3Sensate Gnome
Sensate gnomes are quite powerful. They weren’t really impacted by the Remaster as they serve a very specific purpose that is basically always useful. These gnomes have extremely heightened senses, which gives them an ability: imprecise scent. This means that they can smell a creature (or person) and determine their exact position at a range of 30 feet.
As a consequence of this, due to this special sense, sensate gnomes get a +2 circumstance bonus to Perception checks whenever they’re using their scent to locate a creature inside the aforementioned range.

This means that, for example, if you need to locate a specific person in the middle of a crowded market, you can smell their exact location as long as they’re within 30 feet of you. It also means that, if your GM is trying to get cheeky with some ambushes, you can detect some pesky creature that might be ready to pounce. A sensate gnome will always be useful.
2Fey-Touched Gnome
Versatility is king in a game as ever-changing as Pathfinder, and there are no gnomes as versatile as the fey-touched. These gnomes are fully-infused with fey magic, giving them the fey trait and a useful little tool: an interchangeable cantrip. Fey-touched gnomes can change their cantrip to any other in the primal magical tradition once a day, and it only takes them ten minutes to do so!
While chameleon gnomes can take up to a full hour to change their skin and hair colour, fey-touched can change from a utility to a combat cantrip right before an encounter. They can plug any holes that your party has and can adapt to any situation that your GM concocts, which makes them one of the most powerful gnome heritages.

1Umbral Gnome
Although they get the shortest paragraph out of all gnome heritages in the Player Core book, they are undoubtedly the strongest of them all. From whatever reason you can come-up with when creating your own character, these gnomes have the ability to see in the dark: darkvision. For reference, all other gnome heritages only have dim-light vision.
This means that they are very powerful. They are not blinded when in darkness and can see in it as if they were looking at a normally lit area, except it is in black and white. Darkvision can be obtained in a lot of different ways, through feats, spells, etc. Yet, having the luxury of getting it right from the get-go through an heritage leaves you with the freedom to choose any other available “toys” from those same pools.