Quad9 detection

Is it possible to go to a business’s site and detect whether they have quad9 configured. By this I mean without looking at their DNS settings. It would be great if there is a DNS quad9 “known blocked” domain. ie by browsing that domain you know quad9 is configured and working

Hi, I would be very interested in a test domain as well.

There is no ‘test domain’ currently but to check whether you are protected by Quad9:
On OS X/macOS: go to the terminal app and open a command window, type
dig +short whatismyip.on.quad9.net
if you get an IP address you are on Quad9, if there is no result you are not.
On Windows: open a cmd shell and type
nslookup whatismyip.on.quad9.net
if you get a result you are on Quad9, if you get an error you are not.
Alternatively checking in your DNS settings for and/or