First step would be to use a whois service. You can find these on the web or even run from a command line (>whois domain-name.com).
The output of whois will tell you what the name servers are this will provide a good clue to who the registra is. If the name server point to cloudflare the name servers might be hidden. This is is great for security but not good for your own research.
Whois can also tell you who the regstra and otehr contacts are but increasingly people are chosing (quite rightly) to keep this infomration private.
Trying to contact past developers. ITs and whoever manages the name servers you can see from whois are your final steps.