There are publicly available "Whois" look-up functions which can tell you what organization is providing DNS hosting for a domain name.
For example, you can use the https://whois.com/whois
form. Enter your domain name and it will display a list of publicly available information about the registration of that domain name including who is providing its DNS services.
On the output page, you are looking for the line which begins "Name Servers:".
There should be two or more entries listed beside the "Name Servers:" heading. The DNS systems requires there to be at least two DNS servers, or name servers, that know about each and every domain name. This is for redundancy in case one of the DNS servers is off-line for maintenance or other reasons.
You can usually tell what organization is providing the DNS hosting based upon the domain name used in the name server entries.
For example, any of the domain names which have their DNS hosted with Emerge2 Digital, will have the following three name server addresses listed in their domain name details:
Those are the addresses of each of the three DNS servers which Emerge2 managers on behalf of its clients.
You can tell from those name server addresses, the emerge2.com or emerge2.net is the company behind those name servers.