The agreeable thing to see? (5)
I believe the answer is:
sense
'see?' is the definition.
(seeing is a kind of sensing)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for sense that I've seen before include "Could be common or horse" , "may be common" , "Purport" , "Perceive, detect" , "Perceive - feeling" .)