To whom do cabinet members report to?

The President is required to make occasional reports to Congress about the state of the union. The Constitution does not specify a frequency for these reports, but it is customary to make one every year. Recent Presidents do so in a personal address to a joint session of Congress each January. Past presidents sent their report in writing or made speeches at other times.

One might also say he reports to the people after four years if he runs for re-election and he is subject to impeachment by the House and removal from office after a trial by the Senate if he violates the law or is derelict in his duties.

Other than that, the President is at the top of the organization chart and reports to nobody.