在 + 办公室 + Verb
办公室 means "office," the place where people work. It is a compound noun formed from 办公 (to handle official business) and 室 (room). Use it as a location noun, often with the preposition 在.
他每天早上八点到办公室。
Tā měitiān zǎoshang bā diǎn dào bàngōngshì.
He arrives at the office at eight o'clock every morning.
我的办公室在三楼,你上来找我吧。
Wǒ de bàngōngshì zài sān lóu, nǐ shànglái zhǎo wǒ ba.
My office is on the third floor; come up and find me.
她在办公室加班到很晚才走。
Tā zài bàngōngshì jiābān dào hěn wǎn cái zǒu.
She worked overtime in the office until very late before leaving.