This is an awkward sentence in American English. "How does he do it?" would be the statement I would expect, not sure if that translates well in Polish.
True, but this sentence is designed to teach the word "sposób", so we needed a construction that corresponds well. Mostly, Polish will also use "Jak on to robi?" = "How does he do it?" But if you need to focus on the verb 'way', that's the way.
"which" = który, "what" (adjectival) = jaki
Your sentence makes it sound like there are only, let's say, 4 ways to do it and you're asking which of them was chosen. Which may be correct theoretically, but the original sentence has "jaki", so let's stick to this.