You cannot see the Great Wall from the Moon.
The Moon averages 384,399 kilometres away – from there the wall would look as wide as a hair seen from three kilometres. Even from low orbit, NASA says it is barely detectable. China's first astronaut Yang Liwei said plainly that he did not see it. The wall system was surveyed in 2012 at 21,196.18 kilometres.
Useful: Check every "visible from space" claim with a rough angular-size calculation.
Source: en.wikipedia.org