Some northerners grasp tons I have not taught (9)
I believe the answer is:
intuitive
'not taught' is the definition.
(natural or not needing to be taught)
'some northerners grasp tons i have' is the wordplay.
'some northerners' becomes 'inuit' (the Inuit people of the Arctic).
'grasp' is an insertion indicator.
'tons' becomes 't'.
'i have' becomes 'i've'.
'inuit' going around 't' is 'intuit'.
'intuit'+'ive'='INTUITIVE'
(Other definitions for intuitive that I've seen before include "with instinctive knowledge" , "Using hunch" , "Based on feelings" , "easy to understand" , "Sensed by something other than reason" .)