Best way to detect precise location of a collision on mesh collider?

Say you have a basic, low poly mesh collider made in the shape of a humanoid model. How would you go about detecting the exact location of a collision on that mesh and storing it as a specific location?

In layman's terms: what's the most efficient way to detect if that humanoid mesh has a collision in what would be the right arm, the left leg, the head, etc.