Learn Danish: Hvad vil du bruge opsparingen på når du bliver gammel? - What will you spend the savings on when you get old?

In Danish, når is used for things happening in the future (like 'when you get old') or for things that happen repeatedly ('whenever'). Because getting old is in the future, we must use når. You only use da for a single event that already happened in the past.

Why is there a på right before når, and how does it connect to the rest of the sentence?

It belongs to the verb bruge (to use or spend). In Danish, to 'spend [something] on' is bruge [noget] på. Just like in everyday English, Danish naturally leaves the preposition at the end of the clause when asking a question with Hvad (What).

Why is the verb bliver used to mean 'get' old?

The verb at blive means 'to become' or 'to get' when you are talking about a change in state or condition. So bliver gammel translates perfectly to 'becomes old' or 'gets old'. You cannot use at få (to get/receive) here, because that is only for receiving a physical object or idea.

Does vil mean 'will' or 'want to' in this sentence?

It blends both meanings! The verb at ville often means 'to want to', but it is also used as a helper verb to show future intention ('will'). Here, asking what someone vil bruge (will spend) their savings on is essentially asking what they want or intend to spend it on.