You dont need to define any triggers for a popup menu. Simply attach your pop-up menu to whatever item you want, then use the right mouse button to display the menu.
There is no trigger directly associated with the keyboard. The only way I have found without resorting to a java plug-in is to define a timer that checks if the contents of an item have changed and if so, fires off come code. Using timers is not recommended on web forms, so you would have to use java and some custom-item-event triggers to trap the keyboard events.