Sub-Domain is also a part of a domain. It is associated with the root domain. For example, consider the domain name: demowebsite.com and it can have an unlimited number of Sub-domains. Sub-domains looks like test.demowebsite.com. Likewise, we can create the sub-domain and it is associated with root domain. To view the list of all subdomains in Plesk, run the below command.
plesk bin subdomain -l