"I go to work on Monday."
Particle that Indicates a direction you're moving in. Or a place you're travelling to.
I think に emphasises the destination so on Monday 仕事 is my destination and へ 行きますis the process of getting there with へbeing the journey you take towards the destination.
に is sometimes used to say on. So 月よう日 に here literally translates to "Monday on" = On Monday
You should look up othrr uaes for に for future reference. It can also be used to say in, as in "in this week, i will have finished all my coursework" or something
に has already been used to indicate that it is "On Monday" so to be able to make it directional the particle へ pronounced "え" is used here instead.
should "月よう日に会社へ行きます" not also be accepted? i know that 仕事 (しごと) means "work," but doesn't 会社 (かいしゃ), "workplace," make more sense here as a physical location you travel to?
I think 会社 could also mean office. Since the type of work he's going to is not mention, using a general term for work would be better as not every workplace is in an office. I could be wrong
仕事 = More akin to the word "Job"
会社 = Can be used as office but can also mean company.
I don't know why but Duolingo has set it to only accept 仕事 and nothing else