How would that be pronounced? Would it be pronounced as if it wasn't doubled?
Працюю sounds like праць-у-йу. Soft "ц", then "у", then "й+у" http://forvo.com/word/%D0%BF%D1%80%D0%B0%D1%86%D1%8E%D1%8E/#uk
The stem in працювати is -вати so you remove that and add -ю so it becomes працюю.