Question

I was doing what I should是什么从句？

Answer 1

这句完整版是 I was doing what I should do. 其中主句主语是 I ，was doing则是主句谓语，这样 what I should do在整句中充当宾语（动宾），所以它当然就是（名词性从句中的）宾语从句了。