How do I check if my computer is using the Google Public DNS

You can do the following steps:

1. Start up the command prompt (Win + R, enter cmd and press Enter).

2. At the prompt, enter:

   nslookup
   

The program should display the name and IP address of the default DNS server being used.

I know this is an old question, but I thought I can help with another answer.

I don't completely agree with the answer above. nslookup will show you what DNS you are "supposed" to be using but not necessarily the real DNS you are using. You can configure your computer to use a DNS but your router can hijack the DNS call. In that same note, you can set your router to use a DNS and your service provider can hijack the DNS calls to use their DNS server. (I use a linksys router with tomato firmware in it and with iptables rules I am hijacking all DNS calls to use OpenDNS as the DNS service provider.) If you really want to know what DNS server you are using, I recommend you to google "DNS leak test" and test your DNS. Here is one test you can run: https://www.dnsleaktest.com/