He contributes in a two-way study of the parson's nose (3)
I believe the answer is:
son
'he contributes in a two-way study' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'of the parson's nose' is the wordplay.
'of' says the answer is hidden in the clue.
'SON' is hidden within 'parsons nose'.
Can you help me to learn more?
(Other definitions for son that I've seen before include "Human offspring" , "Young boy" , "Male scion" , "Native" , "A relative" .)