If a body was lying on their back when they died, and was moved to their front after 12 hours, where would one see the skin discoloration from pooling blood?

the parts of the body which is nearest to  the ground ie thier back will show discoloration

Explanation:

If the body remains at a position for long hours, the parts of the body which is nearest to  the ground can develop a skin discoloration as a result of pooling of blood in the tissues and this is called livor mortis, which tends to be permanent from 8Hours upwards.