I don't think the question is "what was the ambassador doing in Benghazi?" or "what was the CIA doing in Benghazi?" They were doing their jobs with the resources they were given. I expect the CIA operates out of every embassy and consulate and has some coordination with the ambassador and his staff in each of them.
The only relevant questions in my mind are "why weren't they given adequate protection?" and "why has 0bama and his administration tried to coverup the fact that this was a terrorist attack with the "video did it" hoax?
John Bolton provides some clarity on who has responsibility for foreign policy.
Bolton Sounds Off on the Congressional Hearing in the Benghazi Terror Attack