Which option correctly completes the sentence: "Let me speak to ___ is waiting for the General."

The key is to decide the pronoun's role inside its own clause: "___ is waiting for the General." Within that clause, the pronoun is the subject of "is waiting," so the subjective form is needed. Therefore "whoever" is correct, even though the whole clause follows the preposition "to." "Whomever" is tempting because it comes after a preposition, but the internal clause function controls the choice here.