The writing on the wall (8)
I believe the answer is:
graffiti
'the writing on the wall' is the definition.
(I've seen this before)
'the writing on' is the wordplay.
I cannot really understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found within the answer.
'writing' could be 'r' (one of the traditional three R's of education) and 'r' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for graffiti that I've seen before include "Mural artwork" , "Wall-scribblings" , "Words or drawings scrawled on walls" , "Unwanted writing in public places" , "Drawing" .)