How to properly denote a nuance between comparing choices


My question relates to how to create the nuance between choosing two or more
methods and knowing which should be the preferred or more suitable choice.

E.g. **"How did you know whether to do/use** 'A' or B?"

＊いつ Aか、Bどちらが使いますか。

At this point, my Japanese is incredibly limited. So I am making more of an
attempt to familiarise myself with different interrogative statements for
those times when I have such questions. Alternatively a different way to say
the same in English may have been :

**"When do you do** 'Method A' or 'Method B'? - This when is similar to 'How
do you know when'.

Thank you for all the help.




いつ Aか、Bどちらが使いますか is unnatural.

I say いつAを使い、いつBを使いますか? If you want to emphasize which one you should use, it
would be いつAを使い、いつBを使うべきですか?




いつ Aか、Bどちらが使いますか is unnatural.

I say いつAを使い、いつBを使いますか? If you want to emphasize which one you should use, it
would be いつAを使い、いつBを使うべきですか?

