The javascript would be in case you are using some plugin that adds custom commands to the main menu or somewhere else, but it sounds like that is not your situation.

To use plugin commands, you will go into any event, add a new event command, on the event command select screen go to tab 3, and all the way on the bottom right you will see "Plugin Command" as an option. From there, a new window will open up where you will choose the Plugin Name, in this case CGMZ Quest System, then the Command Name, in this case Call Scene, and you can also set up any parameters that command may have, but in this case Call Scene does not have any.

Then when you interact with your event, the quest log scene will open up.