How many more people do you have to serve drinks to until you're finished?
How many more rows do you have to pass out 〇〇 until you finish?
例文１ あと何人に飲み物を配ったら終わりますか？
例文２ あと何列〇〇を配ったら終わりますか？
あとどのくらいかを聞くときには、How many more (可算名詞)またはHow much more (不加算名詞)が使えます。
あと何日は、How many more days.
あとどのくらいの時間が残っているかは、How much more time.
日本 
