Damage problem

I suppose the impact is detected with a raycast, which can returns the collider through the RaycastHit parameter. From there, you can access whatever component keeping track of the pnj's hp and apply the weapon's damage to it, as it is probably the component casting the ray in the first place.

But I'm only guessing, given the amount of detail we have to work with.

Here are some pictures how it looks to me hope they help