He has written numerous research papers, but he's not well-known for writing books for the general public. It's possible he's written some academic texts or contributed to edited volumes, but those are not widely available to the public.
If you are looking for specific publications by Nicholas J. Gubser, you can find them on his academic profile pages, such as on Google Scholar or his university website (if he has one).
Let me know if you need further help with your search.