Over and above what's done by doctors (6)
I believe the answer is:
beyond
'over and above' is the definition.
(I've seen this in another clue)
'done by doctors' is the wordplay.
'doctors' indicates anagramming the letters (I've seen 'doctored' mean this).
'done'+'by'='doneby'
'doneby' with letters rearranged gives 'BEYOND'.
'what's' is the link.
(Other definitions for beyond that I've seen before include "Farther than or outside" , "Farther along in space, time or degree" , "Outside the range of" , "unknown" , "On the far side of" .)