Viewer more adventurous — what's being screened? (8)
I believe the answer is:
beholder
'viewer' is the definition.
(thesaurus)
'more adventurous what's being screened?' is the wordplay.
'more adventurous' becomes 'bolder' ('bold' is associated in meaning with 'adventurous').
'what' becomes 'eh' (sound used to ask 'what?' or 'pardon?').
'being screened?' means one lot of letters goes inside another (inserted letters are covered up or screened).
'bolder' placed around 'eh' is 'BEHOLDER'.
(Other definitions for beholder that I've seen before include "there's beauty in her eyes" , "Observer" , "One sees" , "Witness" , "Beauty is said to be in this eye" .)