Hello Kimberly! You ask a great, but kind of complex question.. I'll try to answer it.. So, to start, the difficulty one person might exp in one job, is often completely different for the next person performing the very same tasks.
Example: a brain surgeon is not necessarily going to be a great canvas artist or car salesman. Likewise, a crochet artist might not be a fantastic rocket scientist or correctional officer. Roles like rocket scientist, nano techs, structural engineers & economists often require deep quantitative reasoning & math skills that some ppl would find super easy & others (like myself) couldn't perform even to save their own life, lol.
Alternatively, someone with natural mastery of linguistics & languages arts would be at ease as a professor of higher learning or historical author, in ways that the math wiz's would find way to hard to even consider. Likewise, someone who breezed through an english major or something similar, more than likely wouldn't even consider pursuing a path towards deep space architectural engineering or heart surgery.
Anyways, Im sure you catch my drift. There's no finite way to objectively measure the difficultly or ease each person subjectively experiences in each role. We're all born w/ different natural talents & different learning strengths & weaknesses.
Now, in my exp and in my education as a business coach & researcher, I could probably hazard some educated guesses as to some jobs commonly listed among jobs as requiring extra intellectual, emotional &/or physical fortitude & tenacity from anyone, regardless of natural or learned abilities in any industry in particular. Still, degrees of difficulty for each person & job are still going to vary from person to person.
I would think some of those jobs would be:
Nerve Reattachment Surgeon
Higher Court Judge
National Leader (like POTUS)
Direct Sales Rep
Complaint Depart Rep
Physical/Dev Disabilities Caretaker
Keep in mind, even this list is subjective. There might be some jobs you'd never have included & things you'll add. Either way, I hope this helps answer your question somewhat & helps with whatever was on your mind when you asked =)