Find Contact Point on touch

I know how to find Contact point of collider when object collides with other object using OnCollisionEnter2D(Collision2D other) method.

but suppose i touch on some object, how can i get the contact point on touch?

Every collision has a array of contact points. Each contact point has a position where the collision occured. So you need to get those contact points in order to get the collision position.

void OnCollisionEnter(Collision collision) 
  for(int i = 0; i < collision.contacts.Length; ++i)
    ContactPoint contact = collision.contacts*;*

Collision points:
[Unity - Scripting API: ContactPoint][1]
[1]: Unity - Scripting API: ContactPoint