Most DNS servers have their testing page, where you can run a quick standard test to determine the IP address, hostname, city, country, and ISP.  If you are using OpenDNS, you can test your server at the OpenDNS homepage. Instead of a detailed report, it just shows a yes or a no, confirming whether you are using the service or not. If you are using Cloudflare DNS, you can test your server at the Cloudflare help center. For 1. 1. 1. 1 with Warp, the test page is their help center. It also confirms with a yes/no option stating whether you are using the server or not.  For the AdGuard DNS server, you can log in to their DNS service page and under the AdGuard DNS servers map heading, the page states if you are using the service or not.  For all other DNS services, you can test your server at DNS Leak Test. It gives a detailed report on your server.