This is the 1795th most frequent Russian word.
кого
The word "кого" means "whom" or "of whom" in English, used in the genitive or accusative case.
The word 'кого' is used here as the accusative case of 'кто' (who), referring to the direct object of the sentence.
Кого ты видел вчера?
Who did you see yesterday?
In this sentence, 'кого' is used as the relative pronoun in its accusative form, denoting the person to whom the action pertains.
Он не знает, кого спросить о помощи.
He doesn't know who to ask for help.
Here, 'кого' is used in a context where it signifies the indirect object (the person interested), in the genitive case often required by certain verbs in Russian.