counting score after destroying game object

Hi. I just can't get it working. I tried to see other solutions but I can'T see what I did wrong.

I have a simple game where you just avoid obstacles. Those obstacles travel towards the player (cube). Behind the player I have wall that on collision testroyes obstacle.

I added 3d text and I just don't know how to set it to count score.

 void OnCollisionEnter(Collision col)
 {
     if (col.gameObject.name == "Obstacle(Clone)")
     {
         Destroy(col.gameObject);
     }
 }