Join up two points on catalogue (6)
I believe the answer is:
enlist
'join up' is the definition.
'two points on catalogue' is the wordplay.
'two points' becomes 'en'.
'on' is a charade indicator (letters next to each other).
'catalogue' becomes 'list' (I've seen this before).
'en'+'list'='ENLIST'
(Other definitions for enlist that I've seen before include "Join the army" , "Join the armed services" , "Join up - tinsel (anag)" , "Sign on -- 13 (anag)" , "Obtain help of" .)