laborposteno

Built from laboro and posteno, main root last as always, so the thing is a posteno and labor- says which kind. A posteno on its own is a station, the spot you are posted to, and it carries a faintly military flavour: a sentry stands ĉe sia posteno. Adding labor- civilianises it into a job.

The point of having the compound at all is that the three near-words do different jobs. Laboro is the work itself, the activity: mi havas multe da laboro means I have a lot to do, not that I have several jobs. Laborposteno is the position, the slot in an organisation, the thing you apply for and can lose. Ofico is an office in the sense of a duty held, a role with responsibilities attached rather than a wage. So you serĉas laborpostenon, you faras laboron, and you plenumas oficon.

Shorter alternatives circulate. Posteno alone is often clear enough from context, and dungiteco covers the state of being employed. But laborposteno is the unambiguous one, which is why it is the word that made the frequency list.