This is the 745th most frequent Croatian word.
koga
"Whom" or "who" (in accusative/genitive form).
'Koga' is the object of 'smo vidjeli' (we saw) and indicates the person seen.
Pitao je koga smo vidjeli jučer.
He asked who we saw yesterday.
'Koga' is used as the accusative case of 'who', referring to the direct object of the verb 'voliš' (love).
Koga voliš najviše na svijetu?
Who do you love the most in the world?
'Koga' here is used as the object in a question regarding the action of 'čeka' (waiting for).