A) only when the defender is Evil
B) only when the item is Evil
C) neither A or B
D) both A and B
Same goes for other non-elemental weapon properties such as Axiomatic for Chaotic, Unholy for Good, etc...
The holy damage only accrues when damage is done to an evil target.
Since you aren't sundering the person, it would have no effect.
Also note that the Holy Enhancement specifically says that it deals 2-12 damage against creatures of evil alignment. An Evil sword is not a creature, it is still an object.
An INTELLIGENT evil item, is however, considered a construct and thus a creature, and would take Holy damage.
So, sundering an item held by an evil person does not trigger anything Holy.
Sundering an Unholy Sword wielded by anyone does nothing.
Sundering an intelligent Evil item triggers holy damage.
==Aelryinth