5th dnd – What is the purpose of the Potent Cantrip function of the evocation wizard?

The feature you are talking about indicates the following:

From the 6th level, your dealt damage affects even creatures that avoid the biggest effects. When a creature makes a saving throw against your trap, it suffers half the damage (if any), but does not suffer any additional effect.

There is no mention of evocation spells in the writing. If it worked only on those, he would say it.

For a comparison, see Level 10 Evoker Feature

Authorized evocation

Starting from the 10th level, you can add your Intelligence modifier to a damage roll of any wizard evocation you have launched.

Note that this feature specifically indicates that it only works on evocation spells. And, again, with the second level Evoker Feature

Spell sculpture

Starting at the 2nd level, you can create relative security pockets within the effects of your evocative spells. When you cast an evocation spell that affects other creatures you can see, you can choose a number equal to 1 + the level of the spell. Selected creatures automatically roll their saves against the spell and they suffer no damage if they normally suffer a half damage from a successful rescue.

Source for all quotes

Powerful Cantrip says it works on "canter damage". If it worked only on evoking cantrips, it would rather say something like "evocative cantrips that do damage."

As a result, the following Cantrips of the Core Rulebook are valid under Potent Cantrip:

After you have extended the rest of the rule books, you also add the following items to the list.

  • Create a bonfire
  • Frostbite
  • infection
  • Quick lure
  • Sword shine
  • Thunderclap
  • Toll the Dead

An additional note to add is that the feature does not say that it applies only to Wizard cantrips that you launch. So, if you have access to the Holy Flame or Radiation Word through multiclass or exploits, Potent Cantrip will also apply to those.