Hop solved!
There are 2 different sorting layers. One that is behind the PNJ's, and one that is before it. I check the position of the player when I collide with PNJ's. If the player's position in y> to the PNJ's, then the player is behind it.
It works fine but if 2 PNJ's are too close to one another it doesn't work fine. So it's not perfect but it 's enough for now.
public SpriteRenderer Ren;
void OnTriggerEnter2D(Collider2D other)
{
if (other.CompareTag("PNJ") && other.transform.position.y > transform.position.y)
{
Ren.sortingLayerName = "PlayerDevant";
}
else
{
Ren.sortingLayerName = "PlayerBehind";
}