You can see the list of subdomains below to a specific Target inside the Subdomain Tag.
If you click on Open button you navigate inside the Subdomain page. The Subdomain page contains the tags Dashboard, Agents, Services, and Notes.
Dashboard: you can find all the information about the subdomain with the possibility to add labels to the subdomain and the option to specify if it is the main portal for the target.
Agent: contains the list of Agents that you can run directly into the subdomain, for example, Nmap.
Services: shows the list of services and ports running in the subdomain. Check this link for more details.
Notes: allows you to add notes about the Subdomain. To know more about the Notes check this link.