If you look on the back of the switch, each bay will show the port number that corresponds to it, XG!, XG2, XG3, XG4. First switch in stack, Bay 1, first module =1/XG1, 1/XG2 First switch in stack, Bay 2, second module=1/XG3, 1/XG4 Second switch in stack, Bay 1,first module =2/XG1, 2/XG2 Second switch in stack, Bay 2. second module=2/XG3, 2/XG4 You can also issue the command, console>show interfaces configuration, to get a full list of the ports and their current status.
I have two PC6248 switches stacked.  Switch 1 also has a SPF+ module.   Are these ports XG 1 & XG2 or are they XG3 and XG4.  I did not know if the the ports on the stacking module in slot 1 are considered XG1&2 or not.  Please advise.  Thank you.
PC6248p - xg ports