So he needs to focus on that first and foremost. Lots of online resources with tips for that. Also, the exam sucks and people often fail it 3 or 4 times before passing so I would recommend trying it a few times, but also have a plan b in case he never does. I have a buddy with a Masters in International Affairs, and his only dream was becoming an FSO, but he never could pass the exam, so he is working for the family business now.

That being said, if he does pass, then his resume will help him get a higher placing on the Register. He needs a security clearance so he will need to complete naturalization as soon as possible.