polite: 수고하셨어요 · casual: 수고했어 · leaving: 수고하세요
thank you for your hard work; good work
Example
오늘도 정말 수고하셨습니다. 내일 봐요.
Thank you for all your hard work today. See you tomorrow.
Word parts
수 receive+고 hardship
Literally 'you received hardship' — thanks for the effort.
Good to know
Common at the end of a workday or task. When leaving a shop, people often say 수고하세요.