Investigate, or look again! (8)
I believe the answer is:
research
This clue is a double definition.
'investigate' is the first definition.
(researching is a kind of investigating)
'look again' is the second definition.
('search' can be a synonym for 'look' so perhaps 'research' is OK for 'look again')
'or' is the link.
(Other definitions for research that I've seen before include "Scientific study" , "enquiry" , "Experimentation" , "Investigation designed to expand knowledge" , "Fact-finding" .)