Recently I had to check on a DNS problem at work, and the support person said “the DNS isn’t even pointed at us (the hosting)”. I asked him how he could see that, and the response I received was:
I rely on a Chrome extension that tells me what the IP address is for the particular page I’m on. Everybody has their own way of digging into this.
You can also use a tool like http://leafdns.com/ to get a view of the DNS records for a given parent domain.
I checked the leafdns website and I could see the nameserver error and the IP’s pointed at the domain in question (of course not the correct ones). Filing this here for the next time I need to diagnose / troubleshoot DNS problems.