You can find the folks who are unquestionably the most knowledgeable of C in the usenet group comp.lang.c -- the people who are in the standardization committee (i.e., the group of people who decide how the language should or more importantly should not evolve) lurk there.
Note that compared to heavily moderated forums like JR, you will find folks there quite brazen and curt, and you can find yourself very easily being rubbed the wrong way.
Bottom line: If, in your pursuit of learning or discussing C, you do not mind your ego being bruised, then comp.lang.c is the place for you.
"Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away." -- Antoine de Saint-Exupery