The first question you may be asking is – what’s a dressing gown? No one outside of the UK seems to know. It’s the warm item of clothing you wear after you get out of a bath, or what you put over your pyjamas. Americans call it a bath robe. Still don’t know? OK, I’ll tell you, it’s župan.
Anyway, let’s get back to today’s mistake. In Czech, it seems fine to say, “What means dressing gown?” but in English, you cannot use such a construction. It is wrong. You need to add an auxiliary verb. This word (does) comes after the question word (what), and we also put the main verb (mean) after the noun (dressing gown).
So we say, “What does dressing gown mean?”