This is the 1684th most frequent Polish word.
pracują
"Pracują" means "they work" in English.
Here 'pracują' is used to describe the action of working, attributed to the group 'oni' (they, masculine or mixed gender).
Oni pracują w biurze od rana do wieczora.
They work in the office from morning until evening.
In this question, 'pracują' queries whether the subject, specifically the parents, perform the action of working at the mentioned company.
Czy twoi rodzice pracują w tej firmie?
Do your parents work at this company?
The word 'pracują' is here used to indicate a habitual activity carried out by people globally.