what's the job of a reserved officer in a police headquarters?

Answer 1

A reserve office has a regular job - and gives 8-40 hours a month to the dept they serve - sometimes it's a paid position - sometimes volunteer -

but all are fully trained and sworn officers/deputies

Answer 2

Normally a reserve officer is unpaid and augments the existing force of paid officers. They usually have all the duties and responsibilities of regular officers and require the same level of training but don't get paid.