how to cite an equation that is common knowledge but I use others notation
You seem to have a very mechanistic view of citation, as if there were a set of rules that tell you how to write a citation in every possible (or, at least, common) situation. That's not how it works. Think about what the purposes of citation are, and cite material in a way that is appropriate to those purposes.

Here, there are two intellectual contributions you might wish to cite: the underlying equation and the notation you've used to express it.  If the equation is common knowledge, do you need a citation for it at all? Or would a "see, e.g., [textbook]" or "as introduced by [original source]" citation be more appropriate? Given that you're using the notation throughout your paper, isn't it enough to say once that you use the notation of NW? That gives appropriate credit and informs the reader where they can find more information.