An adherent and he understands what's going on (8)
I believe the answer is:
follower
This clue might be a double definition.
'an adherent' is the first definition.
(I've seen this before)
'he understands what's going on' is the second definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'and' is the link.
Can you help me to learn more?
(Other definitions for follower that I've seen before include "Person who succeeds" , "One accepts the leadership of another" , "A devotee or a pursuer" , "Supporter" , "A loyal adherent - or a pursuer" .)