Genuine manuscript showing spheres of activity (6)
I believe the answer is:
realms
'spheres of activity' is the definition.
'realms' can be an answer for 'spheres' ('realm' can be a synonym of 'sphere'). I'm not sure about the 'of activity' bit.
'genuine manuscript' is the wordplay.
'genuine' becomes 'real' (similar in meaning).
'manuscript' becomes 'ms' (abbreviation for manuscript).
'real'+'ms'='REALMS'
'showing' is the link.
Can you help me to learn more?
(Other definitions for realms that I've seen before include "Kingdoms, or fields of activity" , "Kingdoms, or fields of interest" , "Domains ruled by king or queen" , "Domains - provinces" , "Kingdoms, domains" .)