I've solved with the following code:
Added a unique class on event inside onBeforeEventRender:
args.data.cssClass = args.data.id;
Later, inside onEventRightClick I just look for that class and I activate the popover:
$('.' + event.data.code).webuiPopover({{title: 'sample', content: 'description'})
$('.' + event.data.code).webuiPopover('show')