I am looking for a recipe for the p'tcha my mother made. She used chicken feet instead of calve's feet. It tasted eggy and tangy (from vinegar).

Claudia Roden in "The Book of Jewish Food" provides the recipe for the calve's foot version, but you could improvise with chicken feet. She first blanches the calves feet (I would use the chicken feet and perhaps add some legs so you have some meat to add to the gelatin later)--cover with cold water, bring to the boil, simmer briefly until scum rises, then discard the water. Then, cover again with fresh cold water and seasonings (onion, fresh garlic, dried bay, peppercorns and salt), simmer 3-4 hours until very soft. Strain the liquid. In the bottom of a serving dish or mold, arrange minced garlic, cover with sliced hard boiled egg then the meat from the bones, finally the strained broth. Chill until solidified and serve with vinegar or lemon wedges. (p. 72, The Book of Jewish Food)

No, don't have one but here are some starts.
If you don't find exactly what you want here, some of these recipe authors may have leads for you.
https://www.paleohacks.com/chicken-broth/i-made-chicken-jello-9123
http://www.melaniecooks.com/russian-holodets-meat-jelly-recipe/5063/
https://cookpad.com/us/search/chicken%20feet