PAN-OS SNMP setup is split across a network profile and a management-interface service permission, which trips people up the first time.
Under Device > Server Profiles > SNMP Trap (for traps) or Device > Setup > Operations for read-only polling access, create the profile with your community string or SNMPv3 credentials.
Separately, under Device > Setup > Interfaces > Management, confirm SNMP is checked as an allowed service; the profile alone doesn't open access if the interface itself blocks the protocol.
PAN-OS reports session count, throughput, and HA pair status; for full traffic-based detection rather than just device health, also see the syslog and NetFlow-equivalent guides for exporting session logs.