How do I find and check a domain name's Registrar and where Domain's DNS records are pointing?

First of all, if you are going to change any DNS records, if you don’t know who controls your Domain Name’s records, then you may need to find out who your Domain Name is registered with.
To do that use WHOIS. e.g. https://www.whois.com/whois/

Now this may not be who actually controls your Domain Name’s records, as the Nameservers dictate who controls your DNS settings which include your A record, CNAME records and Mail records e.g. MX etc.
If the nameserver is not your registrar’s nameservers, and this may manifest itself in the fact when you make changes to the records in your domain name’s DNS settings nothing changes, then you must then check who the Nameservers are managed by, and therefore where your DNS records are being managed.

To do that I suggest you use MX Toolbox’s SuperTool and use DNS Check.
https://mxtoolbox.com/SuperTool.aspx

Enter the root domain and select DNS Check from the Orange dropdown button

So that deals with the registrar and nameservers, so now how do you check the status of your A records and CNAME records for your domain name and more importantly your www.domainname.XXX. The easiest way is to use MXTOOLBOX:

https://mxtoolbox.com/DnsLookup.aspx

With this Website you need to check using the Orange DNS Lookup Button, both the root domain e.g. webdadi.com as well as the subdomains e.g
www.webdadi.comto see both the A record (first) and the CNAME records (second) if you type the root domain name in first and the www in front of the domain second.

for the Root Domain normally this will be an A record’s IP Address

For the CNAME record (so any subdomain incl www.) this should say live.webdadi.net