He's learned a vehicle's parked in street (6)
I believe the answer is:
savant
'he's learned' is the definition.
(an extremely clever or learned person)
'a vehicle's parked in street' is the wordplay.
'vehicle' becomes 'van' (van is a kind of vehicle).
'parked in' is an insertion indicator.
'street' becomes 'st' (abbreviation).
'a'+'van'='avan'
'avan' placed inside 'st' is 'SAVANT'.
(Other definitions for savant that I've seen before include "A learned person, from French" , "A learned or wise person from France" , "Intellectual" , "One of great learning" , "Man of great learning" .)