There are two answers to your question, logical and social. The logical answer is 要らない, but that is not socially acceptable. What you should say is 結構です
It can and is used in question forms, but there's actually a huge range. I hear (in everyday speech)
は必要ですか？
は要りますか？
These are more common when it is a direct question about if something is needed.
In many situations, like a restaurant offering something (where it is not entirely "do you need", but a bit of "how about?"), you hear はいかがでしょうか a lot.
