Unfortunately it doesn't look like there is a way to do this right now. None of the api methods that accept an item link return anything that would indicate that it was read. The best you can do is check if the player has already done the quest and then check if the item is in the inventory, but that also doesn't necessarily mean that he has abandoned his humanity and let Valaste get taken (who would ever do that for 2 measly skill points?
).