There is a lot of important stuff that is missing from this question. One of which is whether your DNS server is the authority for your site. I am making some assumptions here.
Assuming that your DNS server is acting as the SOA (authority) for your domain, then you would, I assume since I have no idea what this is for, add an A text record for your site. Your cPanel image seems to be right. You would enter your domain name as
example.com. with the dot at the end and the text as you need to. However, if your DNS is not the authority for your site, then entering the text in cPanel will do nothing. If you are hosting your domain name/IP address in the hosts name servers and this is where your SOA record is, then that is where you need to add the text record. If your registrar is where your domain name/IP address is hosted and this is where your SOA record is, then this is where you need to add the text record.
How you can know who your SOA is? Simply (assuming linux) use:
dig example.com any
If you still no not see a SOA record, then use:
dig +trace example.com any
You should see one now since the +trace is looking for the SOA specifically and will only accept an answer from the SOA.
On a side note: NEVER host public DNS and FTP on the same server as your website. These are often used in reflection attacks and other exploits to gain access to your web server. Once done, you are toast and may never know it. Remember that not all hackers tip their hat. In fact, most don't. If you are not intending to make your DNS public, then firewall it. ACLs help, but are not enough stop all attacks.