The Feature does not only apply to Evocation Spells
The feature you are talking about says the following:
Starting at 6th level, your damaging cantrips affect even creatures that avoid the brunt of the effect. When a creature succeeds on a saving throw against your cantrip, the creature takes half the cantrip’s damage (if any) but suffers no additional effect from the cantrip.
There is no mention of Evocation spells in the write-up. If it only worked on those, it would say so.
For comparison, see the Level 10 Evoker Feature
Beginning at 10th level, you can add your Intelligence modifier to one damage roll of any wizard evocation spell you cast.
Note how this feature specifically says it only works on Evocation Spells. And, again, with the Second-level Evoker Feature
Beginning at 2nd level, you can create pockets of relative safety within the effects of your evocation spells. When you cast an evocation spell that affects other creatures that you can see, you can choose a number of them equal to 1 + the spell’s level. The chosen creatures automatically succeed on their saving throws against the spell, and they take no damage if they would normally take half damage on a successful save.
Source for all quotes
Potent Cantrip says that it works on "damaging cantrips." If it only worked on Evocation Cantrips, it would instead say something like "Evocation cantrips that deal damage."
Therefore, the following Cantrips from the Core Rulebook are valid under Potent Cantrip:
Once you extend out to the rest of the Rulebooks, you also add the following to the list.
An additional note to add is that the feature does not say it only applies to wizard cantrips that you cast. So if you gain access to Sacred Flame or Word of Radiance through Multiclassing or Feats, Potent Cantrip would apply to those as well.