6 (?) - form depends on the case used:
N kto? co?
G kogo? czego?
D komu? czemu?
A kogo? co?
I (z) kim? (z) czym?
L (o) kim? (o) czym?
So there are basicly 4 different form of 'kto' 'co', but the same forms need different cases.
I don't think there is a section for the question words above. My advice is: try asking questions when you encounter a sentence that uses nouns in Gen, Dat, Acc ..:
Kaczka idzie z psem (Instrumental) (A duck is walking with a dog) - Z kim(czym) idzie kaczka?