Questions & Answers about On és el teu passaport?
On means where.
It is the normal Catalan question word used to ask about location:
- On és...? = Where is ...?
- On vius? = Where do you live?
So in this sentence, On introduces the location question.
Catalan normally puts the question word first, just like English often does:
- On és el teu passaport? = Where is your passport?
So the basic order is:
- On
- verb
- subject
- verb
This is very natural in Catalan.
A form like És on... would not be the normal way to ask this question.