Stand next to a disc jockey who's got nothing trendy on (6)
I believe the answer is:
adjoin
'stand next to a' is the definition.
I can't judge whether this definition defines the answer.
'disc jockey who's got nothing trendy on' is the wordplay.
'disc jockey' becomes 'dj' (synonyms).
'who's got' becomes 'a' (I can't justify this - if you can you should believe this answer much more).
'nothing' becomes 'O' (O resembles 0).
'trendy' becomes 'in' ('in' can mean fashionable).
'on' is an insertion indicator (as in clothing 'on' a person).
'a'+'o'+'in'='aoin'
'dj' inserted inside 'aoin' is 'ADJOIN'.
Can you help me to learn more?
(Other definitions for adjoin that I've seen before include "Meet - touch" , "20 down" , "Be next to (something)" , "Lie adjacent to another" , "Interconnect" .)