If B6 can issue a boarding pass for the JFK-DOH flight, then it should indicate Pre-Check. It will be a B6 boarding pass, so although it will allow you to get through security a little quicker (IF they can issue it, that is...), you will still need to collect a QR boarding pass.

You can't enter your KTN on a QR booking, as QR doesn't participate in Pre-Check.