出工 is a separable verb (离合词) meaning 'to go to work' or 'to show up for a work shift,' especially in contexts where labor is assigned (farming, construction, factory). The verb 出 and the object 工 can split: you insert aspect markers (了, 过), duration, or frequency between them — e.g. 出了三天工 ('went to work for three days'), 出过一次工 ('showed up for work once'). It's more concrete than the general 上班, often used for physical or day-labor work.