のを知っていますか

「のを知っていますか」is used to ask the listener if they know about the content before の. The particle accompanying the subject of the clause before の changes from は to が.
「Nを知っていますか」is used to ask the listener if they know about the object N.
Regarding the response, it's important to differentiate between「知りません」and「知りませんでした」. Specifically, you respond with「知りません」when you don't know about the information asked, even after hearing the question. On the other hand, you respond with「知りませんでした」when you originally didn't know about the information asked, but upon hearing the question, you now know about it because the information is included in the question.