Learn Croatian: Je li napravio doručak?

Croatian doesn't use a 'do/did' helper verb for questions. Instead, it uses the question phrase Je li followed by the past tense verb napravio (made). Literally, it's like asking 'Is it that (he) made...?'

How do we know it means 'Did he make' if there is no word for 'he' (on)?

The verb napravio ends in -o, which is the specific past tense ending for a single male. That tells us the missing subject is 'he'. If the hidden subject was 'she', the verb would be napravila.

Why doesn't the word doručak change its ending, since it is the object receiving the action?

Doručak (breakfast) is a masculine noun. In Croatian, when a masculine noun is an inanimate object (a thing, not a living being), its object form (the accusative case) stays exactly the same as its basic dictionary form.

Could we use Da li instead of Je li for this question?

Yes, you will often hear people say Da li je napravio doručak? in everyday speech. However, starting with Je li is considered the more standard and proper way to form yes/no questions in written and formal Croatian.