The effect of pig's trotters and skin jelly on supplementing human collagen is the same, the only difference is that the human body digests and absorbs the collagen in skin jelly more easily.
This is because when making skin jelly, the pig's skin is first boiled into a liquid and then frozen. The boiling process completely breaks down the structure of the pig's skin into small fragments.
Although the human body's digestive function for protein is basically adequate, if we process the collagen before consumption (for example, by making it into skin jelly), breaking the protein from large molecules into small fragments, the body's digestion and absorption of it will be relatively easier.