Meaning: This sentence means that if a talented person is lazy, someone with less talent but who works hard can achieve more.
Choice of Words: Hard work means putting in a lot of effort and dedication. Trump means to defeat or win a competition. Talent means a natural ability to do something well. Slumber means to sleep deeply. When you put them together, "Hard work trumps talent when talent slumbers" means that hard work and dedication can overcome natural talent if the talented person is not working hard.