At least once.
Lots of people have "lots of moles
", and that, in and of itself, is no big deal.
But he should have a thorough exam by a dermatologist, who will determine if any of them need to be removed, and how often he needs to be reexamined after that. Between exams, though, if any mole starts to itch, bleed, change color, or grow suddenly, he'll need to get back to the dermatologist pronto.