Skull Studies - Learning Structure 

Not 100% sure what you're asking, but I will try to answer what I think you're asking. I have not tried the riley method. Also apart from very obvious landmarks, eyes, nose, teeth, there aren't that many, and there's even fewer you can see on the surface with muscles/skin on top. Though you need to learn the skull, the muscles are equally important if not more so. They will help you relate what you see on a face to the skull beneath and also understand the planes of the face and why they form. For example, your teeth usually rest a bit below your lower lip, even in open mouths you almost never see as much of the lower teeth as the top. The general shape/planes of the mouth is given by the muscles, but if someone bites differently (overbite/underbite), the overall appearance can change a lot. Your cheeks and how much fat there is in that area, affects how sharp the cheek bones look. The only place where the skull matters more is in the forehead where there's little muscle. Usually the shapes there and around the eyebrows in neutral expressions are given entirely by the bone beneath, for example, look up the temporal bridge, the frontal eminence, and the suborbital process. You can usually see these quite clearly in most people. And from the side, you can usually see the cheek bone going from the ear to the cheek. As for the proportions, it's a matter of practice. If you can draw what you see in proportion as you practice drawing different faces, you will notice they all have some proportions in common, and others not (you can then use these to add character by changing them). If you cannot draw what you see in proportion (or close enough), then I would suggest you focus on practicing that first with more basic shapes/objects.