请对这句话就划线部分提问：The woman under the tree is Li Lei’s mother。

Where is the woman who is Li Lei's mother?

Under the tree是地点状语，对地点提问就要使用疑问词Where。
显然此句被提问对象是那个woman，但为了保持原句的表达内容不缺少，加上定语从句who is Li Lei's mother来修饰主语woman

这句话翻译为：那个是李磊母亲的女士在哪里？

Where is Li Lei's mother?

Where is the woman who is Li Lei's mother?