As per the jQuery docs for .on:
Deprecated in jQuery 1.8, removed in 1.9: The name "hover" used as a
shorthand for the string "mouseenter mouseleave". It attaches a single
event handler for those two events, and the handler must examine
event.type to determine whether the event is mouseenter or mouseleave.
Do not confuse the "hover" pseudo-event-name with the .hover() method,
which accepts one or two functions
So you need to replace with mouseenter and mouseleave events:
$('#front-container').on("mouseenter mouseleave", "#jobs-by-cat .job", function () {
$(this).find('.hover').toggleClass('hidden');
});