Question

That was the new personnel manager _____ everyone speaks so highly

Answer 1

That was the new personnel manager _____ everyone speaks so highly.

So the answer in the blank is who with

Answer 2

Answer:

That was the new personnel manager of whom everyone speaks so highly.

Explanation:

This sentence is missing a preposition. A preposition connects the subject to the object. In this case, we do not know  if the manager is the same manager of whom everyone speaks so highly, therefore we have to add the preposition 'of who'.