If I skip native language, maths and English as the obvious ones for everyday existence, I'd say history.
I'm in technology field, so no connection with my job.
However, in my country the history is teaching the big timeline of the world, and it is fascinating how the human kind got to the place it is now, how people lived their lives earlier, how the few influential ones crossed the rivers and destroyed big empires, how the alliances in the world were shifting, what human kind is capable of.
History is necessary to understand a lot of art and it is a big part of understanding the world around me.