No, The Nun II is not on Netflix, and it likely won't be any time soon, seeing as it is going to stream on Max. In the meantime, you'll just have to head out to a theater or wait for it to become available on streaming and VOD.
Talk about why he wants to see the movie.\n\n The R-rating doesn't ban children under 17 from a movie, it restricts them to watching it with a parent or guardian (and includes a recommendation that parents and guardians learn more before allowing their child to see the movie).
However, if the theater sold you a ticket to an R-rated movie, even though you're under 17 and not accompanied by an adult, then you have a right to be there. If you are removed, the theater will likely have to refund your ticket.