You could go about it in different ways. Lets say the area entering the area of the player is a small one, say of a bullet. Then you can emit the area entered signal from the bullet, and send with it the global position of the bullet. Then if the object recieving the signal also knows the global position of the player, you can calculate the difference, and what you get is the local position of the bullet, relative to the player.
If the area is a bigger one, you can do the same thing of course, but the position you end up getting might not end up being so close to the area of the player.