That's an interesting question. Is he applying to a job for his time or ours? It must be our time because technically he applied for the job of King in his own time and failed at it miserably. :)
So if Macbeth were to apply for a job in today's world, I would say it might be with the military because he is a warrior. He might be good at being a spy along with his wife because they plot well together. On the other hand, both couldn't handle the guilt of killing people so that might not be good for them. How about a corrupt CEO mishandling people's trust and money? Or maybe he'd make for a good cowardly terrorist. :)
If this is a question for an essay, you could take some of the suggestions I gave and come up with examples from the text that help to characterize these skills/jobs. If it is for a short answer response, see if your teacher wants you to quote anything from the play or simply reflect on some fun ideas. Basically what they are looking for is some critical thinking on your part that analyzes Macbeth's character and personality in relation to today's job market.
President of a small country? :)
Also check out the enotes.com character analysis of Macbeth for further insight into his character and personality.