When adding the SNMP Traffic Sensor to your device, you'll see the live graph within it's "Live Data" tab. Note that the device needs to support SNMP accordingly. If your switch also supports a Flow protocol, you can use the various flow sensors. It will then show the overall traffic going through the appliance. Using Maps, you can add all those graphs to one accumulated overview.
Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.