When you use the ready-made bookmark, "I've cooked this" it opens up a few extra fields, Cooked On and Note. I guess there are a few different ways to get to that bookmark in the first place--I use the little gray chef's hat to the left of the recipe title, which then turns to green after you've saved the "I've cooked this" bookmark and its associated fields.
But, like the OP said, I don't know how to view this information after it has been entered.