Person who sees nothing left in people (6)
I believe the answer is:
oracle
'person who sees' is the definition.
(someone who can see the future)
'nothing left in people' is the wordplay.
'nothing' becomes 'O' (O resembles 0).
'left' becomes 'L' (common abbreviation).
'in' indicates putting letters inside.
'people' becomes 'race' (people can mean a national group or race).
'l' going into 'race' is 'racle'.
'o'+'racle'='ORACLE'
(Other definitions for oracle that I've seen before include "Shrine; its message" , "Person regarded as source of knowledge, like old Greek prophet" , "Authoritative statement" , "Medium of divine revelation" , "Augury" .)