It would be nice if there was a "Goto Definition" option in the context menu when you right clicked on a word. The Function List already has an index of the file's variables and functions. On a right-click, it could check what word is under the cursor and then perform a lookup in it's index list. if there is a match, then provide the option to jump to the definition just as if you had double clicked on the entry in the function list… similar to visual studio's options.
Initially it would be good enough to start with just allowing the user to jump around in the current file. Maybe once things are working there, an option to search for and jump to a function in all opened documents could be included if it doesn't cause a big performance hit. I wouldn't expect it to be able to search all files in a directory because there isn't a "project" concept in N++ to identify all the source files for a particular project (and shouldn't be).