where is/are my daughters?
我女儿们可能在同一个地方 也可能在不同的地方
where are my daughters. 这句话很明显my daughters是主语。在这种特殊疑问句里,有正常语序和倒装语序两种结构。
正常语序,比如:Who phoned last night? 这种句子的主语就是Who,把句子变成陈述句就是 Sb. phoned last night.
倒装语序,比如: Who are you talking about?这种句子主语是 you. 把句子还原就是, you are talking about who.
你举的这个例子,主语是my daughter 不是where,还原是 my daughter is in/at somewhere. 所以不用纠结的哈~~