This function can be used to get the x position of the sprite element in the room. You give the sprite element ID (which you get when you create a sprite element using layer_sprite_create() or when you use the function layer_sprite_get_id()), and the function will return the x position value.
Argument Description sprite_element_id The unique ID value of the sprite element to get the information from
var lay_id = layer_get_id("sprite_sky");
var spr_id = layer_sprite_get_id(lay_id, "Clouds");
if layer_sprite_get_x(spr_id) < 0
The above code will get the layer ID for the layer named "sprite_sky" and then use that to get the ID of the sprite element on that layer. This ID is then used to check the element x position and if it is less than 0, then the layer element is moved to a different x position.