CHA, INT, OR WIS

You are skilled in a specific job, specialty, or creative art. You know how to use the tools of your trade, how to perform the profession’s daily tasks, how to supervise helpers, and how to handle common problems.

Each job is a different specialization and you can not learn the main skill, only specializations.

While skills like Culture, Life Science, Mysticism, and Physical Science represent highly specialized fields of study, a Profession skill represents an aptitude in a vocation requiring a broader range of less specific knowledge. When you put ranks in a Profession skill, you must choose the ability score keyed to that skill: Charisma, Intelligence, or Wisdom.

Note that many of the Charisma based skills are instead Perform( actor, artist, comedian, dancer, musician, orator, poet and such), and some are bluff(con artist), but some are just professional skills like courtesan, politician and similar.

Note that many Intelligence based skills are actually other skills like Physical science(lab technician, Scientist), Life science(Biologist,archaeologist), computer(Info sec specialist, vidgamer), Electronics, Engineering and so on, but some are just Intelligence-based Professions like accountant, architect , corporate professional, lawyer, mathematician, philosopher, professor, psychologist.

Note that many Wisdom based skills are actually other skills like Life Science(cook), Survival(Herbalist, Animal trainer), Engineering(Maintenance worker) and so onand so on, but some are just Wisdom-based Professions like bounty hunter, counselor, dockworker, farmer, gambler, general contractor, manager, mercenary, merchant, miner.

You can use Profession or any of the other professions like the the others above with other skills to earn money as a job

You can use your professional skill to recall facts related to the profession.

Often different professional skills might know the facts but might have different DCs.

As an example both a corporate professional and a lawyer might know about business contracts, but obviously the lawyer would have easier time to find the legal loopholes in such.