Knowing with gear change, you get greasepaint (7)
I believe the answer is:
sapient
'knowing' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for sapient that I've seen before include "Literary word for wise" , "Discerning" , "Snipe at, being wise" , "Snipe at (anag.)" , "Having intelligence" .)