OMGPI does not have any complicated event API. If you want to use any of bukkit event that is not in OMGPI, the Game class is automatically registered onEnable(), so you can just use @EventHandler for those.

However, some events are better to use in OMGPI:

First is event_preGamefigSave(Gamefig gamefig) - here you can set some values. Example - gamefig.setUnpresent("key", value); - set something in the gamefig. Similarly, you can do event_preMapfigSave() to set some mapfig values. Another way to set stuff in config that is unpresent - setUnpresent("section", "key", value, "key", value...) - will set values in the section if the section does not exist.

For many events there are methods called event_something, for player events event_player_something, and so on. To see all events look at JavaDocs.