I would say that it should be occupationS. The issue gets confusing as it can sound like you are implying that each person has more that one occupation. But basically it should be occupationS .

Hi, Nikolay! In this sentence, it's more natural to use "occupations" in plural form because it is far more likely that the group of people being referred to works different occupations. However, by asking in singular form, the person asking is implying that all of them share the same occupation. Is that the context of this sentence?

The word occupation has different form in different situations.If it means job, it is countable so you can say occupations.but if it means "when someone lives or stays in a building or place it is uncountable.