一番アルコールの低い酒は何ですかって英語でなんて言うの？

The two questions you see provided above are terrific ways to ask someone which drink has the smallest amount of alcohol. In the first question you will notice the word proof. The proof of an alcohol is the strength is has. The higher the number, the stronger the alcohol will be. This word is used for straight alcohol, like whiskey or rum. This word is not used for mixed drinks. If you want to ask about mixed drinks the second question would be appropriate.

Native speakers will say like this: “What is the weakest alcohol drink you have?”.
There are lots of other ways to say it, but this one is the most accurate and most commonly used.
Here is an example on how to use this in a conversation:
A: Excuse me, waiter. What is the weakest alcohol drink you have here?
B: We have light beer, it has the least amount of alcohol.

When you want to ask for a drink with the least alcohol then you would use the words lowest/least amount
So you could say 'What drink is the lowest in alcohol?' or 'What drink has the least alcohol?'

When you want to ask for an alcoholic beverage that the the least amount of alcohol; then you may ask in the following ways:
-Which drink has the weakest alcohol?
-I'd like a light wine/beer
-I would like a drink with the weakest alcohol

"Which drink has the lowest alcohol content?"

The drink that has the lowest alcohol content is also the one with the lowest alcohol.

Which drink has the least alcohol percentage on your menu?
This question is a common way to find out which alcohol is not very strong.
For example
Customer in restaurant - Which drink has the least alcohol percentage on your menu?
Waiter - This beer here in the menu sir has the least alcohol.

Hope this helps