The importance of “for” or “to” while a question is getting asked.

I have a Canadian teacher and I asked him that. He said: “Although “Where to buy” is understood firstly, you can also answer that question as “I want to buy a book to read somewhere”.

That’s because question words in English belong to the best sensible place as meaning. Therefore, Your first answer must be: “I want to buy a book somewhere to read” but If your second answer is “I want to buy a book to read somewhere”, It’s not incorrect gramatically even though it is not more expected than last one.

What do you think now?