Trade fair certain to get publicity (8)
I believe the answer is:
exposure
'publicity' is the definition.
(I've seen this before)
'trade fair certain' is the wordplay.
'trade fair' 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 "Revelation (of something secret)" , "Uncovering" , "public attention" , "Risk for Antarctic explorer" , "O pure sex! (anag.)" .)