You don't need academic knowledge of anatomy if you grow up in a culture (that of medieval peasants) where hunting, cleaning, and cooking animals was likely common. Much can be inferred from analogy, in the way the non-human dissections were (and still are) used for training surgeons.
Probably. Clearly if you happen to have a butcher at hand to get you the liver. Not sure if nowadays you could just bring a random dig to a butcher and ket him extract the liver for you - might be hygienic standards preventing to do it. Earlier might be the belief that dogs are dirty etc. but i don’t know...