This is the 3590th most frequent Polish word.
czego
"Of what" or "of which."
The word 'czego' functions as a genitive form of 'co' (what), asking about the object in a specific context.
Czego chcesz na obiad?
What do you want for lunch?
Here 'czego' is also in the genitive form of 'co', linked with the verb 'szukać' (to search), which requires the genitive case.
Nie wiem, czego on szuka.
I don't know what he's looking for.
In this example, 'czego' represents the genitive case used with the verb 'bać się' (to be afraid of), which takes objects in the genitive case.