If we are willing to find authors of one subject we first need to find articles. I would like to know if it is possible to find the author who wrote the most article on one subject? Is it possible on Pubmed?
I am not aware of how to do this without finding all the articles on a topic (hopefully narrow) and count the old fashioned way. The NLM does provide some help and they might have a way, so I would encourage you to click on the 'Contact' button at the bottom of the PubMed page and ask if they can help you with this question.
I believe Scopus would help with your quest. Meanwhile just as indicated by Robert John Wolff, there's a need to first search for the topic and identified a few most common authors. Thereafter, author search tool in Scopus can then be used to get more detail information about each of those authors and their respective number of publications.
The link here should somehow help: https://guides.lib.umich.edu/citation/Scopus