jquery trigger hover on anchor

You are on the right track, the problem is the extra # in the selector, just remove the first hash:

$("a#trigger").trigger('mouseenter');

Note that since IDs must be unique, there is no need to specify the element type, $('#trigger') is more efficient.

Also note that:

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.