I don't know what he's really thinking 里的 's代表什么?

I don't know what he's really thinking 里的 's代表什么?
I don't know what he's really thinking 里的 's代表什么?

I don't know what he's really thinking 里的 's代表什么?
is
因为后面接的是thinking （动名词）

be动词is
“我不知道他真正怎么想的”

is

he is

我不知道他真正的想法.

be动词iS.我不知道他真正的想法.