China built a wall...
This is another Trump Meme. This meme refers to Trump's wall, and uses false logic to say that since China built a wall and China has very few Mexicans, the US should build a wall if they also want fewer Mexicans,
Additionally, the image is animated to show Trump's face looking shocked, and then reconsidering , and then accepting the idea. I am pretty sure that the text on the meme is supposed to have been said by Trump.
Now, why is this funny?
The logic is absurd - yes, the first statement is true, but the implied causative effect is not true - correlation does not equal causation.
The second funny part is the animated image of trump making facial expressions. His face is pretty expressive, and multiple of his expressions are silly. It is hard to quantify exactly why they are silly, but it is probably because they are more expressive than most people's face is most of the time.