German phrase
Welches ~ wird für ~ verwendet?
Meaning
Which ___ is used for ___?
When to use it
It asks what is used. This polite, neutral phrase suits questions about items and their purpose.
Example dialogue
Welches Dokument wird für das Visum verwendet?
Which document is used for the visa?
Für das Visum wird in der Regel der Antrag benötigt.
The application is usually needed for the visa.