How to check my custom Dynamic DNS is being used and not my ISP DNS?

I've set up a FreeDNS thing, see the image:


But how do I actually check I am going through this DNS and not my ISPs? Is that even the function of this, or does it do something else? I googled around for how to do it but all the various command prompt commands that supposedly tell you what your DNS is just report my router as the DNS, fail to even work, or don't show anything to do with the DNS.

Thanks in advance.