Find a Component/GameObject Using an Interface Reference

An interface is not attached to something. A class can implement an interface. An interface basically acts like a seperate base class. So at any time you can cast the reference to the actual type if you know it. If all classes that implement are MonoBehaviour scripts you can always cast the reference to MonoBehaviour or Component. This gives you access to "transform" or "gameObject". If you want to access more specific things you would need to know the actual type so you can cast the reference accordingly

The easiest way is to use an "as"-cast in conjunction with a null check.

 MonoBehaviour mb = damagable as MonoBehaviour;
 if (mb != null)
 {
     GameObject g = mb.gameObject;
     // [...]
 }

Another way this can be done if you don't want to cast would be to have the interface create a blank function like getGameObject that returns a GameObject. The implementing class would have to define what the function does and can return its gameObject.

 public interface interfaceName {
 
      GameObject getGameObject();
 
 }
 
 public class className : MonoBehavior, interfaceName {
 
      public GameObject getGameObject() {
           return gameObject;
      }
 
 }