First, it this really grammatical in English? I'm not a native speaker, but I'd say you need a predicate if you use 'how': 'How elegant is the suit!'.
Second, your variant is different grammatically from the Ukrainian sentence: what ≈ який, how ≈ як. However, in this exact sentence наскільки 'how much' works better: «Наскі́льки костю́м елега́нтний!» 'How elegant the suit is!'. Since the original sentence uses «яки́й», it's better translated with 'what'