Check the material in script [C#]

You can get the renderer on your cube, then ask it for the material:

 //find the game object using whatever means you like
 GameObject target_object = WhateverCodeYouUseToGetTarget();
 
 //get the renderer from the object
 MeshRenderer target_renderer = target_object.GetComponent<MeshRenderer>();
 
 //get the material from the renderer
 Material target_material = target_renderer.material;
 
 //do something based on the material
 if(target_material.name == "cow")
 {
     //do stuff if pointing at a cow!
 }

That's a fairly basic example - might be a couple of compile errors cos I don't have unity to hand!

Note that if you aren't certain the target object will have a mesh renderer, you should add some checks to make sure it isn't null.