Jargon taken down — an unknown amount to work out (12)
I believe the answer is:
gobbledygook
'jargon' is the definition.
(gobbledygook is a kind of jargon)
'taken down an unknown amount to work out' is the wordplay.
I cannot really understand how this works, but
'taken' could be 'led' (to lead someone somewhere is to take them there) and 'led' is found in the answer.
'unknown' could be 'y' (algebra) and 'y' is located in the answer.
'amount' could be 'go' (go is a kind of amount) and 'go' is present in the answer.
'work' could be 'go' (synonyms) and 'go' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for gobbledygook that I've seen before include "bunk?" , "Officialese" , "Nonsense!" , "Meaningless language" .)