The Handler Counter function is on the SCRIPT-TOOLS palette, button number 4. It builds a list of the handlers in the current card-script, background-script, and stack-script. It then displays this in a list. Command-clicking on the name of a handler in the list will open the appropriate script, type command-G to see the script.
If you do not wish to see all these script lists, then hold down the option key as you click the handle count button. This will bring up a dialog, click set to choose which scripts to search.
