Belonging to circuit, needless to say (2,6)
I believe the answer is:
of course
'needless to say' is the definition.
'belonging to circuit' is the wordplay.
'belonging to' becomes 'of' ('of' can mean 'belonging to' or 'owned by').
'circuit' becomes 'course' (I can't justify this - if you can you should give a lot more credence to this answer).
'of'+'course'='OF COURSE'
Can you help me to learn more?
(Other definitions for of course that I've seen before include "Naturally, certainly" , "Assuredly, without doubt" , "'Naturally, as might be expected (2,6)'" , "Naturally, goes without saying" , "Without a doubt, as was to be expected" .)