1、We haven't settled the question of whether it is necessary

1、We haven't settled the question of whether it is necessary for him to study abroad.
为什么这句是同位语从句而不是宾语从句,不是of后面跟的是宾语吗?
2、(1)People in part of North China sleep on ______ they call "kang".
(2)The rescue team got to _____ was once a famous scenic spot which fell into ruins in the terrible storm.
为何这两句下划线处都应填what 而不填which?能仔细说说what 和 which的区别吗?

1、We haven't settled the question of whether it is necessary for him to study abroad.
你说的也很有道理,从局部看,whether it is necessary for him to study abroad 确实是介词 of 的宾语从句.但是,从介词短语（介词+宾语从句）of whether it is necessary ...来看,它们是用来进一步说明 question 的,貌似 question 的同位语,但是却不能解释为同位语从句,而是 question 的后置定语,提到的是“什么样的问题”,也就是本题说的“是否他有必要出国学习的问题”.
2、what 和 which 在意思上和用法上很不相同,区别如下：
1）用作代词时,what 指的是不同性质的事物中的特定的一个,即指“什么性质的”；而 which 指的是若干个同类事物中的具体的一个,即“哪一个”.
2）what 可以用作连接代词,引导名词性从句（主语从句、表语从句、表语从句）,等于“不言自明的先行词+关系代词that/which”,相当于汉语的“所...的事情/东西/言语等”.下面的题目就是这种用法.
(1) People in part of North China sleep on ______ they call "kang".
句子中的 what they call "kang"（他们称其为“炕”这种东西）是介词 on 的宾语从句.这里的 what 称作关系代词性连接代词,等于先行词 the thing + 关系代词 that/which.如果把这个从句改写为定语从句,就成了——
People in part of North China sleep on the thing that/which they call "kang".华北地区的部分人睡在他们称其为“炕”的这种东西上.
另如：
I don't understand what you say = I don't understand the words that/which you say.
(2) The rescue team got to _____ was once a famous scenic spot which fell into ruins in the terrible storm.
同上题一样,这里的 what 等于先行词 the place + that/which ,可以改写为
The rescue team got to the place that/which was once a famous scenic spot .（救援队到达了一处曾经是著名景点的地方）.
在这种情况下,如果单用,只能用 what（如原题）；如果改写为定语从句,则需要添加关系代词后用关系代词 which（如改写后的句子）.