German phrase
Für welche ~ gilt ~?
Meaning
Which ___ can ___ be used for?
When to use it
Ask what something covers. Use it to check limits or permitted uses.
Example dialogue
Für welche Züge gilt dieses Ticket?
Which trains can this ticket be used for?
Es gilt nur für Regionalzüge, nicht für Fernzüge.
It is only valid for regional trains, not long-distance trains.