You can go to system and Compare two Values like Enemy.Count <= 0 that if you want to make something happen if there is no enemy
but if you want to know how much enemy are in layout just make a text and set the text to enemy.Count this will display the quantity of enemy on layout.
[Object].Count - will count all the object that exist inside or outside the layout and will get it quantity as and int.
hope this help ya Good Luck!