There are thousands of memes that DNS is the cause of (almost) all computer issues, so debugging DNS issues is necessary more often than anyone would like. One question that comes up often when debugging DNS is: Which server is my actual DNS resolver? An easy way I found to answer this question is the whoami tool of Akamai.
whoami.ds.akahelp.net will always respond with the IP address of the requesting server.
$ dig +short TXT whoami.ds.akahelp.net "ns" "203.0.113.1"