From the Administration Panels open the Reports Panel at your Backoffice, right click and choose Net Trading-Symbols Types Report, choose the desired period and click on the desired office or IB on the tree and you will see its name on the title bar for net trading report then click report. At the bottom of the generated report you will see the commission for every symbol or the total commission for spots and futures.

Another way to do that:
Go to the desired office, group or IB on the Accounts Tree and pess right click and choose Statement(s) then choose the desired period then click report. At the bottom of the generated page you will see the total commission for the requested office or IB.