Auditor finally hears half of text on board ship (8)
I believe the answer is:
listener
'auditor' is the definition.
(I know that auditor can be written as listener)
'finally hears half of text on board ship' is the wordplay.
'finally' says to take the final letters.
'half of' means to take half the letters.
'on board' means one lot of letters goes inside another (inserted letters are taken on board).
'ship' becomes 'liner' (liner is a kind of ship).
The last letter of 'hears' is 's'.
'text' cut in half is 'te'.
's'+'te'='ste'
'ste' inserted inside 'liner' is 'LISTENER'.
(Other definitions for listener that I've seen before include "Hearer" , "One paying attention" , "One lending an ear" , "One being attentive to sounds" , "Someone paying attention" .)