is this format of question correct and what is the alternative style?
For what this instrument is used?
Thanks in advance.
If you say “For what this instrument is used” I would understand you, but I would think that English is not your native language. More common would be: “What is this instrument used for?” or even “For what is this instrument used?”
When forming a question, we invert the subject and verb: “this instruent is” -> “is this instrument”