For those who don't know (https://en.wikipedia.org/wiki/Ontology), an ontologist is someone who specializes in organizing concepts into groups and hierarchies, but also higher-order structures. Taxonomist is a related line of work.
In today's tech scene, people with this skillset seem to most often be tasked with designing and building out structured knowledge graphs. Several of the individuals I know also have experience writing Lisp.
This is a fairly niche category, which is why I'm posting it separately from the recent job threads. Please let me know if you have any leads.