Question

با کی کار داری؟

با چه کسی کار دارید ؟

.

 

Answer 1

Whom do you ask for? (formal)

To whom do you wish to speak? (formal)

Who do you wish to speak to? 

https://en.oxforddictionaries.com/usage/who-or-whom

Answer 2

(May I ask)who are you looking for?

Answer 3

http://idioms.thefreedictionary.com/With+whom+do+you+wish+to+speak%3F

"With whom do you wish to speak?

Who do you want to talk to?

مورد اول formal و مورد دوم informal است.

Answer 4

Whom do you want (to talk to)?