For question 1 it has to be equipment and it has to be metal, note the name of the item both in lore and shop is Djin Metal Vessel. They must be some kind of metal object, frem a bracelet, ring, pendant to a dagger or even and arrow head. They are objects the dying Djin used to place part of themselves in.
As for question 2 that is still in internal debate due to this worlds lore and how that works as most of such said items have been destroyed and by who will be revealed much much much later in the rp.