Resident needs study, principally investigating form of Buddhism (7)
I believe the answer is:
denizen
'resident' is the definition.
(I know that resident can be written as denizen)
'study principally investigating form of buddhism' is the wordplay.
'study' becomes 'den' (term for a study or office).
'principally' suggests taking the first letters.
'form of buddhism' becomes 'zen' (Zen is a school of Buddhism).
The initial letter of 'investigating' is 'i'.
'den'+'i'+'zen'='DENIZEN'
'needs' is the link.
(Other definitions for denizen that I've seen before include "Inhabitant (of the deep?)" , "Dweller" , "Enid Zen (anag) - inhabitant of a particular place" , "Person in foreign country enjoying rights of natives" , "Resident" .)