Packet Monitor takes a deeper look at application traffic. SonicOS captures or mirrors the traffic according to the settings you have configured on the MONITOR | Tools & Monitors > Packet Monitor page, when:
App Rules policies created on POLICY | Rules and Policies> App Rules page use an action object with Packet Monitor action type.
Access Rules policies created on the POLICY | Rules and policies > Access Rules page that use Packet Monitor.
The default is to create a capture file, which you can view with Wireshark™.