Standards-wise of course @MujjinGun is correct. But the standard transliteration of my own name in English is Cheong and no one's ever said it right. (It sounds more like Jung.) The word Korea itself comes from 고려 which sounds like "goh-ryuh" but got transliterated as "kor-yo," which resulted in me believing old Korea was called 골요 until... 2 minutes ago.
So, if the goal is fidelity to pronunciation by modern tongue, then as a Korean who went to a community-run 中文学校 for some years I agree with @Nocturnez's answer,
But I wanted to add my own answer to explain a couple things.
Strangely, the real vowel sound is somewhere between @MujjinGun's ㅗ (as in "door") and @Nocturnez's ㅜ (as in "tool"). I say "strangely" because I never would have logically thought there was a sound "between" those two, which even the Korean graphemes ㅗ and ㅜ suggest are opposites. Your mouth shapes like you're going to say "oo" but it sounds more like "oo". (Got that?)
Now pictorially there is the ㅡ (as in "dungeon") that appears to be neither ㅗ or ㅜ and arguably is "between." Which is totally irrelevant reasoning, but interestingly in order to prounounce 中, there is a hint of that ㅡ sound in addition to the strange mix of ㅗ and ㅜ! Just goes to show how mindbogglingly complex phonetics can be.
As for the consonant, ㅉ is absolutely closer to correct than ㅈ.
The real sound is somewhere between the following 3...
쭝, 쫑, 쯩
and the following 2 even though I didn't dive into this one...
Some say I was destined to write this answer, since the word in question is a homonym of my own name 정원일 (鄭元一) in each language...