Do you know who will come tomorrow?（who是主语）I don't know who is his father.这句话有点怪。我们一般可以理解为：his father is who的。Who are you？这个who是表语的。习惯认为who还是表语，所以下面的句子正确的：I don't know who his father is.（who是表语）He wanted to know what had happened the night before.（what主）判断方法：改成特殊疑问句，没有“助动词+主语+谓语”结构的，或者说是what,who,which后面直接...
