1.1.1.1 doesn't need to resolve. It is a DNS server. It's an open, recursive public DNS server, ala Google's 8.8.8.8, or OpenDNS, etc.

$ dig news.ycombinator.com 1.1.1.1 +short

news.ycombinator.com.cdn.cloudflare.net.

104.20.43.44

104.20.44.44

Edit: It occurs to me you mean reverse resolution. A dig +trace seems to stop at ns3|7.cloudfare.com.