It's a question of how much you want to go into detail, and how much detail you know to avoid. First step is to get the proportions and relations of skull, ribcage and hip right, to get a convincing torso, then you need decent shortcuts for major limbs, joints, feet and hand. At that level you will be able to draw quite convincing outlines of pretty much all figures, which is not a small feat. If you are able to do this with clean lines, you will be at the level, that is used in a lot of older comic books.
It's only once you want to add a lot of details and shading, that you get into the problem of having to understand in more detail what muscles and bones underneath the skin exactly cause all those little bumps and ditches to appear (and then you also need to look into details of lighting, like core shades, reflected lights, highlights, etc.). Adding more details also gives the viewer more comparison points to spot where your proportions are slightly off. It looks great if you can pull it off, and probably everyone dreams about being able to add a thousand perfect details, but it's also the way to ruin perfectly decent drawings by "overworking" them.
Learning landmarks and improving your understanding of anatomy is essentially the same process. If you really have no clue at all how the bone structures look, that these landmarks indicate, you should probably look them up, and maybe try to simplify and draw them a few times just as geometric shapes from several angles. If you have troubles simplifying them (the hip bone is a bugger for example) search for other artists simplification.
Finding those landmarks on the reference, and starting to visualize how the underlying structure must be placed, still takes a lot of practice, and starts with quite an amount of guesswork. The end goal isn't to draw pretty landmarks, but to improve your understanding of anatomy by searching for them. Most of them won't be visible anyway once people wear clothes, or when they are simply behind other parts of the body, etc. So, when you feel like you have troubles learning the landmarks due to lack of anatomy skills, you are approaching the horse from the wrong side. Landmarks are just a tool towards learning anatomy.
Thanks for your reply. Honestly I havent had a straight mind over figurative art. Neither I am sure about how to be productive and visualize over apply all that I ha e learned over figure drawing from youtube videos from Stan but I am not exactly able to put it on page. Although my gesture drawing have improved over the last months so that one of the few good things I guess...