To give a clue as to who manages a domain's DNS records you need to perform a whois search. This will return a list of NS records. These NS records will often be descriptive enough to inform of at least where the NS records are located e.g. ns1.blacknight.com
Tip: Replacing the subdomain of the NS record with "www" will often bring you to the main website of the company hosting the DNS records for that domain
However, sometimes the hostname is not descriptive enough and adding www. to the domain yields no results. In these cases you need to continue running whois searches on the NS records themselves to find out who manages/owns those domains.
Note: Learning where the DNS records are located only gives a clue as to whom manages those records. For example, the DNS records may be hosted on Blacknight's nameservers but your IT company might be the people actively managing those records.