"Apád" is a bit harsher than "apukád". Cf. "Anyád!" is used as a curse, short for "kurva anyád", which is really not nice, while "anyukád" is a nice way to refer to that somebody else's mother. This word order emphasises "apukád", i.e your interested where the father works, not the mother. "Hol dolgozik apukád?" would emphasise the where (e.g. you were already talking about his father). Also "édesapa" and "édesanya" are a bit more formal and nice way to refer to mothers and fathers, e.g "Édesapád hol dolgozik?"