This is the 4706th most frequent Polish word.
nazwisku
"Last name" or "surname."
Here, 'nazwisku' is used in the locative case, indicating the relation of 'having a question about the surname.' It relates to the inquiry regarding the surname in the context.
Mam pytanie o jego nazwisku.
I have a question about his surname.
In this construction, 'nazwisku' appears in the locative case again, with the preposition 'o' that governs the locative case in Polish to indicate the discussion subject, which is the surname mentioned.
Rozmawiałem z nim o nazwisku, które mi podał.
I spoke to him about the surname he gave me.
Here, 'nazwisku' is used in the locative case once more within a phrase that references subjects connected to a surname. It indicates matters associated with the surname.