How does wNAF work with prime finite fields?
The scalar is a scalar, it is not uncommon to view it in $\mathbb{Z}$ instead of in a field defined by the order of the curve/point (note:it does never make sense to view it in a binary field). 

So $d\mod2$ becomes the least significant bit of $d$ and $\frac{d}{2}$ becomes the same thing as $floor(\frac{d}{2})$ which is the same thing as a right shift by 1.