Learn Croatian: Gdje je ona?

Yes! Croatian is a pro-drop language, meaning you can often drop the subject pronoun. Gdje je? translates to "Where is he/she/it?". Adding ona makes it specifically "Where is she?", which you use when you need clarity or want to add emphasis.

Why isn't the order Gdje ona je?

The word je (is) is a clitic, which is a special type of unstressed word. In Croatian, clitics must go in the second position of a sentence. Since the question word Gdje takes the first spot, je must immediately follow it, pushing ona to the end.

Is je the only way to say "is"?

je is the short, unstressed form of the verb biti (to be) for "he/she/it". This is the form you will use most of the time. There is also a longer, stressed form (jest), but je is the one you will rely on for everyday sentences and questions like this.

How would I change this to ask "Where are you?"

You would swap the clitic je (is) for si (are), making it Gdje si?. Notice how we usually drop the pronoun ti (you) because si already makes it completely clear who you are talking to.