"What juice do you want?"
By itself 汁 means "juice" in the sence of "fluid" or "sauce". When meaning a fruit juice it's either 果汁 or the specific juice 苹果汁, 橙汁 etc. (I don't think I've ever heard 汁 alone in this context) But in English it's normally shortened to simply "juice". Admittedly it takes some "reading between the lines" but that's language learning.