That book is a bout what? Should be good too, isn't it
Does about (sobre) always come before the object?
Would ¨O que é esse livro sobre? ¨ be correct?
In often acceptable to place a preposition at the end of a sentence in English, but in Portuguese, it's incorrect to do so.
actually, it is a question of prepositios in question. it usually comes at the beginning of the sentence. (esse livro é sobre...). for instance: com quem você vai? (who are you going with?) para quem é isso? (who is it for?)
Is the definite article "o" necessary here?
Yes. What = o que