Explanation
According to the Palo Alto Networks documentation, the Server Monitoring panel displays the status of the servers that the User-ID agent monitors for user mapping information. The graphic shows that the User-ID agent is connected to a server with the IP address 10.1.1.10 and the name lab-client, which is a domain controller (DC) according to the Type column. Therefore, the correct answer is A.
The other options are inaccurate or incorrect based on the graphic:
The host lab-client has been found by a domain controller: This option is inaccurate because lab-client is not a host, but a domain controller itself. The graphic does not show any information about hosts being found by domain controllers.
The host lab-client has been found by the User-ID agent: This option is incorrect because lab-client is not a host, but a domain controller itself. The graphic shows that the User-ID agent is connected to lab-client, not that it has found it.
The User-ID agent is connected to the firewall labeled lab-client: This option is incorrect because lab-client is not a firewall, but a domain controller. The graphicshows that the User-ID agent is connected to lab-client as a server, not as a firewall.
References: :
https://docs.paloaltonetworks.com/pan-os/9-1/pan-os-web-interface-help/user-identification/device-user-identific