how/why should ... ?used to express surprise that something has happened or that someone has asked you a particular question 怎么会/为什么会…？〔用于表示惊讶〕 Why should anyone want to marry Tony? 怎么竟然会有人意嫁给托尼？
Don’t ask me. How should I know? 别问我，我怎么会知道？
→ how/why should ... ? at should(3)