Any object you want to check the position of should be in a group. You could then iterate through the nodes in that group and check their position against the one you're looking for.
func kill_node_at_pos( pos=Vector2(100,52) ):
for node in get_tree().get_nodes_in_group("guffins"):
if node.get_pos() == pos:
This most likely will be an ineffective way of doing what you're doing, unless you're quantizing your positions in some way. If the node is at position (100, 52.00001) it will fail the check.