As usually in C, you start from the name, then try to go to the right until you hit parenthesis, then go to the left until parenthesis, rinse and repeat.

So, first, the name:

    memset_ptr

Then, try going to the right, but aha! before we can really gain speed, a parenthesis is immediately blocking us. We shrug off the bruises and turn to the left:

    (* const volatile memset_ptr)

"Hey guys, memset_ptr is a volatile const pointer..." Now, we hit left parenthesis, so we're again allowed to go right, yay!...

    (* const volatile memset_ptr)(void *, int, size_t)

"...to a function taking such-and-such arguments..." Uh, oh, the equal sign, so no more to read to the right; disappointed, we turn back to the left for the final run:

    static void * (* const volatile memset_ptr)(void *, int, size_t)

"...returning a pointer to void! Hah, got you! Simple, really. No arrays, no pointers to pointers, not even a function pointer returning a function pointer, meh. Uh, oh, aaaaand, yes, by the way, the variable is static, so, like, file-local, um. Yeah, yeah, I saw it from the beginning, oh, go away, you're just picky. And, and, you wouldn't recognize a function returning a pointer to an array of pointers to functions returning anonymous struct even if it hit you in the face, pfff!"