Question

With whom do the doctors identify charlie?

by "whom" is referring to another person?

I don't get this question. Please clarify. thanks.

Answer 1

We use "who" when the word is being used as a subject of a verb or a complement (predicate nominative).

We use "whom" when the word is being used as any kind of object -- direct object, object of a preposition, etc.

In this sentence, "whom" is the object of the preposition "with." The informal way to phrase this idea is as follows:
Who do the doctors identify Charlie with? (Two grammatical errors in there, but people still understand it!)

In that sentence, Charlie is one person, and the doctors are another set of people. The word "whom" is a third person being referred to.