Object - your coin.
Layer - layer where you want the coin to appear.
Image point - image point of Enemy object. "0" would be its origin image point.
It's a common method of spawning and it should work.
Try running your game in Debug Mode (Ctrl-F4), you'll be able to see what's going on. You'll see if the number of coins increases after an enemy is destroyed, where on the layout each coin is located etc.