Touch Range for PeVi vs active magical spell

If I want to dispel a spell that is currently affecting a target (i.e. has a duration longer than momentary), is it sufficient to cast a PeVi spell at Touch range and touch the target? Or is it even possible to "touch" a spell you have not cast? Would you have to use Voice range instead?

Yes, that would be sufficient. But note, that the touched Target might resist your PeVi spell.