there is a function/something called break point
this will makes you able to stop by some code if the code flow reached there
break point on the packet handlers
trace until the action is done
go back and repeat that again stepping inside where it's done
repeat all of that until you find what you are looking for
else go to the client ini files , get the id or even to the db and get to skills and get it's id and search the entire solution for it
about gm commands , this commands are just a method that is called whenever you start your msg string with special char (most common @)
it convert all chars to lower case then check for sub strings which is predefined by you to do certain stuff
same goes for that too , break on the handlers until it takes you to the chat packet , step inside the check , read the commands
else just search for any command you know in term of "command" with the quotes and you should land there
but honestly you can't just own a server and don't know how to get that done
i feel sorry for myself downloading your client for couple of hrs to find exploits :\