Joomla loadmodule or loadposition inside CiviCRM
I don't think that you can do that, at least not without programming. Event descriptions and profile intro fields are rendered by CiviCRM, not Joomla, and CiviCRM does not process Joomla plugins.

If you have the event page linked to a Joomla menu item then of course you can display a module elsewhere on the page (outside of the CiviCRM-generated content).