कः meaning (masculine) who, what
का meaning (feminine) who, what
किम् meaning (neuter) who, what

All these three means the same in sanskrit. Only gender varies. According to the context it means who or what.
Even for non-living things कः, का are used. Same way किम् is used for living beings too.
These can be used only in singular (एकवचनम्)

सः कः? – Who is he?
रामः कः? – Who is Ram?
नृपः कः?- Who is the king?
ॠषिः कः – Who is the sage?
कः आगच्छति? – Who is coming?
पुस्तकम् कः प्रेषयति? – Who is sending the book?
भारत देशस्य कः प्रधानमन्त्री? – Who is the Prime Minister of India?
भवान् कः? (पु.)-Who are you?
वाटिकायाम् कः क्रिडति?-Who is playing in the park?
गानम् / गीतम् कः गायति? – Who is singing the song?
बालकः कः? – Who is the boy?
त्वम् कः? – Who are you?
समयः कः? – What time is it?
नियमः कः? – What rule?
कः देवालयः? – What temple?
कः कार्यालयः? – What office?
भवती का? (स्त्रि.)-Who are you?
त्वम् का? (स्त्रि)-Who are you?
सा का? – Who is she?
बालकः किम् खादति? What is the child eating?
युवकः किम् नयति? – What is the youth taking?
किम् मित्रम्? – Who is friend?