[Jeopar]

Surgeon is a very challenging profession because most of the time the operation is about life or death. To perform under the stress and time constraint is very challenging.

[Greenleaf]

Soldiers who serves their nation is definitely a challenging profession.

[Miamoo]

Any job will be a challenging one if you don't love your work. So it depends on your interest in work. If you love what you do, your work is just a breeze, however tough and back breaking it may be. On the contrary, if you are not happy with your job, you will find it challenging however simple or easy your job is.