Simple, you save game before you hatch the egg. once the egg is hatched you can check out the pokemon, then you soft rest the game. You now know what is in the egg while it is still in the egg. Since the stats gender and so on are set once you pick up the egg and not when it is hatched. How ever as said I will trade you the egg for any random pokemon so you can check it out your self.... and once you have can trade the ditto for said random pokemon holding the dawn stone.