Subjects he's met going around (6)
I believe the answer is:
themes
'subjects' is the definition.
(I know this)
'he's met going around' is the wordplay.
'going around' indicates anagramming the letters.
'hes'+'met'='hesmet'
'hesmet' is an anagram of 'THEMES'.
(Other definitions for themes that I've seen before include "Topics, ideas, motifs" , "Motifs, subjects" , "Subjects or repeated melodies" , "Subject matters, motifs" , "items proposed for discussion" .)