1. Go to https://mxtoolbox.com/DNSLookup.aspx - write the domain you want to check - and press enter:
Let's take covid19.rs as an example domain in this tutorial:
2. Click on IP shown on the previous screenshot, it would lead us to Reverse DNS lookup (PTR), so on this page we can see what is the hostname of that server:
If it is your server, here is how to find on what account the domain is located: viewtopic.php?f=17&t=603