#You can't, it's private.
You can't, it's private.
Now, that's not the end of things, as I suspect that wasn't really your question.
Firstly, you need a reference to this script. Which you can get from a reference to the game object this script is attached to. GameObject.Find() works sometimes, I don't recommend it, but none the less, once you have the GameObject reference...
Game_Scene_Script sceneScript = gameObj.GetComponent<Game_Scene_Script>();
int score = sceneScript.GetScore();
Of course, that still means you need to either make the Score public or provide an accessor function, GetScore().
public int GetScore() {
return Score;
}