It's very common to use French words in English when you are talking about cooking. The more pretentious and expensive the restaurant, the more likely it is to use French. We generally approximate the French words to something that sounds OK in English (just as the French do with English words!) . I agree that 'au jus' is pronounced as 'oh joo', with the 'j' as the same sound as in the middle of 'measure' or 'pleasure'. It's a posh way of saying 'with gravy'.

It'll be something like "哦" and a mix of "许 -- 句"

This is a French word meaning 'with juice'. If meat is served 'au jus', it is served in the juices that come out of the meat during cooking. To pronounce it, it would sound like 'Oh joo' but the 'j' would have a sound we don't have in English, like the 'j' in Bonjour.

US: It's pretty common (even in non-fancy places). I'd say it's pronounced closer to [o ʒu].

Let's see，next, we got roast beef au jus.Who's got-the roast beef au jus? Stella, beautiful.-Bon appetit, Stella.