In ITMS 7.6 there are some views allowing to collect information about agent connectivity with Notification Server.
vAC_AgentHealth and based on it
vAC_AgentCommunicationHealth - view returning latest communication time from agent to Notification Server ,
vAC_AgentConfigurationHealth - view returning latest time when agent requested configuration policy from Notification server
vAC_AgentBasicInventoryHealth - view returning latest time when Notification Server received basic inventory from agent.