"주인은 동업자에게 말해요."
Translation:The owner speaks to their partner.
Can someone explain why all these partners or types of people you work with begin with 동?
They're people that do stuff WITH you, like the (Latin-derived) prefix co- in English.
If it's "their partner" shouldn't "the owner" be plural, or "their" could/should be changed to "the" for it to be grammatical correct
can't say with certainty whether this is grammatically correct, but it's now definitely common practice to use "their" with singular nouns to avoid having to specify the person's gender (or when you're unsure of someone's gender). takes some getting used to, but is definitely a convenient way of using pronouns
The first written record of they/them/theirs in the (pseudo-)singular is in 1375. (I say pseudo because it falls short of grammatically passing for he/she/it. e.g. *They comes in each day.) I think some guides had been nitpicking its usage until very recently (partially out of ignorance of both its lengthy historical usage and its importance to modern speaker needs). However, I think it's "there" and is acceptable or defensible in formal writing.
Because we don't know their gender. 'They' is a gender neutral way to refer to someone.