Span Port Monitor Sessions

Monitor Sessions - This is very handy, if you have a spare port on the Cisco, you can use Wireshark to monitor this port, you can then monitor any other port on the Cisco from here.
Enter the following commands to setup monitor ports.
monitor session 1 source interface gigabitEthernet 0/x (where x is the port you are connected)
monitor session 1 destination interface gigabitEthernet 0/x (where x is the port you wish to monitor)
monitor session 1 source interface gigabitEthernet 0/10
monitor session 1 destination interface gigabitEthernet 0/23
The above two lines will setup port 23 on the Cisco for monitoring, on port 23 you will see any traffic that is on Cisco port 10.

no monitor session { session_number | all | local | remote }

The above command stops any sessions (no monitor session all)
https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750x_3560x/software/release/12-2_55_se/configuration/guide/3750xscg/swspan.html