Learn Croatian: Gdje je brat sada? - Where is brother now?

je is a special type of word called an enclitic (a weak word with no stress of its own). In Croatian, enclitics almost always have to take the second position in a sentence. Since Gdje is the first word, je naturally locks into the second spot.

Why is there no word for "the" or "my" before brat?

Croatian doesn't have articles like "the" or "a". If you mean "the brother", it's just brat. Also, native speakers often leave out possessive words like "my" (moj) if it's obvious from the context whose brother it is.

Could I change the order of the last two words and say Gdje je sada brat?

Yes! Croatian word order is quite flexible. Gdje je sada brat? is perfectly correct and means exactly the same thing. The only strict rule is keeping the weak verb je in the second position.

I have seen the word for "now" written as sad. Is sada exactly the same?

Yes, sad and sada mean the exact same thing. You can use them interchangeably. The choice usually just depends on the rhythm of the sentence or the speaker's personal preference.