This little script creates a Maya’s Muscle Surface Attach as close as possible to a given locator.
First it creates the Surface Attach node and links it to the geometry. Then, through the Closest Point On Mesh node, it finds  the respective Face and then two opposing Edges of that face to info for the Surface Attach. On the last step it goes through UV iterations of the Surface Attach node and finds which of the four corners of that face is closest to the given locator.