High Elf
Cantrip. You know one cantrip of your choice from the Wizard spell list. Intelligence is your spellcasting ability for it.
Half-Elf
Cantrip (High Elf Heritage). You know one cantrip of your choice from the wizard spell list. Intelligence is your spellcasting ability for it.
As per the Race, the cantrip you picked will use your intelligence modifier. Other races that get casting typically have a clause for that, for example most innate casting abilities (Tiefling, Yuan Ti, etc) use Charisma as the modifier.