Taiwan belongs to China,that is everybody knows这句话对吗why?

错的,这句话里有两个谓语,没有连接词
that引导非限制性从句是不可以的
要用which
Taiwan belongs to China,which everybody knows.
That Taiwan belongs to China is what everybody knows.
It is known to all that Taiwan belongs to all.
这些表述都对

前半句对了，后半句有点像中文
As we all know, Taiwan belongs to China.

belong只用于主动式

It is known that taiwan belongs to China.