kernighan-and-ritchie - 15 questions
kr-c - 25 questions
knr - 29 questions
I suggest we merge kernighan-and-ritchie -> knr and kr-c -> knr.
Rationale: knr seems to be the most popular tag, and I believe these tags all mean the same thing. knr is just an abbreviated form of kernighan-and-ritchie, and all questions tagged knr are also tagged c, so kr-c seems redundant. Also note that all questions tagged kr-c are also tagged c as well, and some are tagged knr too.
knr
being the merge target. It has a tag wiki now.