Gained knowledge of new rental (6)
I believe the answer is:
learnt
'gained knowledge' is the definition.
(I've seen this before)
'new rental' is the wordplay.
'new' is an anagram indicator.
'rental' is an anagram of 'LEARNT'.
'of' acts as a link.
(Other definitions for learnt that I've seen before include "Heard" , "Picked up" , "Acquired knowledge or skill" , "Realised" , "Gained knowledge or skill" .)