Moral expert I see probing this when detained by alien (8)
I believe the answer is:
ethicist
'moral expert' is the definition.
(I've seen this before)
'i see probing this when detained by alien' is the wordplay.
'see' becomes 'C' (the word for the letter, according to Chambers).
'probing' indicates putting letters inside (probe can mean to poke or prod into).
'when detained by' indicates putting letters inside.
'alien' becomes 'et' (extra terrestrial).
'i'+'c'='ic'
'ic' inserted into 'this' is 'thicis'.
'thicis' inserted within 'et' is 'ETHICIST'.
(Other definitions for ethicist that I've seen before include "Moralist" , "Moral expert" .)