Smart doctor leads study that has no answer (6)
I believe the answer is:
dressy
'smart doctor leads study that has no answer' is the definition.
'dressy' can be an answer for 'smart' (I've seen this before). I'm not certain of the rest of the definition.
'smart doctor leads' is the wordplay.
'smart' becomes 'essy' (I can't justify this - if you can you should believe this answer much more).
'doctor' becomes 'dr' (abbreviation).
'leads' is a charade indicator (letters next to each other) (some letters go in front of others).
'essy' after 'dr' is 'DRESSY'.
Can you help me to learn more?
(Other definitions for dressy that I've seen before include "Wearing stylish clothes, elegant (6)" , "Formal or elegant" , "swish" , "Sartorially elegant" , "Nattily attired, wearing stylish clothes" .)