哪门子 is a colloquial phrase that functions as an interrogative pronoun, mainly used in rhetorical questions to express dissatisfaction, disbelief, or contempt. It roughly corresponds to 'what?' or 'why?' in English, but carries a dismissive tone. The structure is similar to 'what kind of…?' in questions like 'what kind of logic is that?'. It is not used in neutral or polite inquiries—only when the speaker disagrees or thinks something is nonsense.