Try penetrating cunning jargon (5)
I believe the answer is:
argot
'jargon' is the definition.
(argot can mean jargon or slang)
'try penetrating cunning' is the wordplay.
'try' becomes 'go' (both can mean an attempt).
'penetrating' indicates putting letters inside.
'cunning' becomes 'art' (I've seen this in another clue).
'go' going inside 'art' is 'ARGOT'.
(Other definitions for argot that I've seen before include "Special language of a groat?" , "Kind of slang" , "Patois, vernacular" , "Jargon or slang (of a group)" , "Language of a particular group" .)