I have a Catalyst 4500 L3 Switch Software (cat4500e UNIVERSAL-M), Version 03.02.00.XO RELEASE SOFTWARE (fc2). So I just wanted to verify that the switch only does dot1q encapsulation because the switchport trunk encapsulation dot1q command does not work. Is this documented somewhere.
Depends on your linecard (not the supervisor card).
Some line card will only support 802.1Q so entering the command will result in an error message.
As what Glen has posted, if you enter the command "sh interface