noun
staff member; official; station employee
Refers to a person who works at a public office, station, or institute. 署員 is typical for police/fire stations; 所員 for research institutes or offices.
警察署の署員が現場に駆けつけた。
Police station staff rushed to the scene.
研究所の所員が新しい論文を
A member of the research institute published a new paper.
職員 is a broader term for any staff member in an organization, while 署員/所員 specifically refers to members of a 署 (station) or 所 (office/institute).
Compound of 署 (station/office) or 所 (place/office) + 員 (member). The reading しょいん is shared by both kanji forms.