"Where do they live?"
I don't think there's any difference in meaning and that the choice is up to personal preference. That said, you'd probably be more likely to hear 哪儿 in the Beijing dialect and northwest dialects in general.9
I really wish to know it too, I don't even know how the two pinyin are different
Can somebody explain to me when to use zhu? Because some sentence use zhu while some are not.