Large exhibition certain to get publicity (8)
I believe the answer is:
exposure
'publicity' is the definition.
(I've seen this before)
'large exhibition certain' is the wordplay.
'large exhibition' becomes 'expo' (I've seen this before).
'certain' becomes 'sure' ('sure' can be a synonym of 'certain').
'expo'+'sure'='EXPOSURE'
'to get' acts as a link.
(Other definitions for exposure that I've seen before include "Vulnerability; photograph" , "Uncovering" , "Lack of cover" , "illness caused by cold" , "Display (or removal) of protection" .)