I'm pretty sure if it was Xi Jinping's "private notebook", then it would have been written in Chinese. So, regardless of the fact that Trump is functionally illiterate, he still wouldn't have been able to read it.
And if it was in English...then he definitely left it there on purpose, knowing that Trump could sneak a peek.
Xi’s notebook would be in Chinese. Except for the bits he wanted Donald to read.
Xi's private honey pot
Hunny
I'm assuming the Chinese did a little psychological test and Trump turned out to be the little bastard without self control that eat the cookie while he thought noone was looking.
Viral Post Claims
On one of the embedded tweets:
The folio/folder clearly shows the symbol with the shape of the U.S. presidential seal printed on the front. In this video, President Trump picked up the exact folio at his left hand side on the table as he walk up to give his toast speech at the 33'55'' of this video [links]
Links got truncated when I copied them but you can click them on the article