名词性从句包括主语从句,宾语从句,表语从句和同位语从句.
whether用于主语从句：
Whether I knew John doesn't matter.
whether用于宾语从句：
It all depends on whether we can get their cooperation.（注意：本句it是代词）
whether用于表语从句：
The question is whether we can finish our work by tomorrow evening.
whether用于同位语从句：
The question,whether we need it,has not yet been considered.