It's a "leadingleading" question or an "interrogatinginterrogating" question. It is designed to prompt a specific confirmatory response.
However, if those seem too general or insufficient, you might consider "verifyingverifying", "substantiatingsubstantiating", or "confirmatoryconfirmatory" as adequate answers. The truth is already known and verification/confirmation is sought.
6.You respond, "That was a(n) verifying question"
6.You respond, "That was a(n) confirmatory question"
https://en.wikipedia.org/wiki/Leading_question
https://www.thefreedictionary.com/interrogating
https://www.thefreedictionary.com/verifying
https://www.thefreedictionary.com/confirmatory