Honestly I'd keep it a nail, but make it more of a nail than a dagger. As it is it kind of curves off to the side, giving it more of a wicked daggery look. But thematically, nails pop up a LOT in holy scriptures and the iconography of them aside is pretty metal.
To make it more nail-like, I think you'd just have to straghten it out then give it a tapering point at the very end.
As for what you ASKED: For folds, I find it handy to think of where the fabric would "catch" on the leg. For example, here it'd catch on the right knee and foot and the left knee and shin. From those points, you'd create a curve, and use that to extrapolate the fold of the fabric. And remember, the less folds the heavier the material, so if you're going for burlap or heavy robes try to limit how many you put in and if you're going for more of a cloth or silk feel, add more!
