Seeing what you have to say for youself (3-7)
I believe the answer is:
lip-reading
'seeing' is the definition.
Both the answer and definition are singular nouns.
Perhaps you can see an association between them that I can't see?
'you have to say for youself' is the wordplay.
I cannot really understand how this works, but
'have' could be 'read' (reading is a kind of having) and 'read' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'what' is the link.
Can you help me to learn more?
(Another definition for lip-reading that I've seen is " Interpretation by following mouth movements".)