Prerequisite: Requires the Roguish Archetype Arcane Trickster
When you hit a target with a Spell that targets only one creature and is incapable of targeting more than one creature, and requires you to make a Spell Attack, you can add your Sneak Attack Damage if all other criteria are met.
Your wording is really off, but I really like the concept.
Try something like this:
"Picking this feat, you gain the ability to add your Sneak Attack Damage to single target Spell attacks. All the regular sneak attack rules must apply for this to happen."
I really like the idea of this feet, and kind of what i was hoping to find interesting things that add a twist to a playstyles. Monkeybussinezz is right and the grammer could be adjusted to fit the schematics of traditional feets but its a great idea.