Declaim, though having nothing to complain about (5)
I believe the answer is:
orate
'declaim though' is the definition.
'orate' can be an answer for 'declaim' (I've seen this in another clue). I am unsure of the 'though' bit.
'nothing to complain about' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'to complain about' becomes 'rate' (I am not sure about this - if you are sure you should believe this answer much more).
'o'+'rate'='ORATE'
'having' is the link.
Can you help me to learn more?
(Other definitions for orate that I've seen before include "Harangue" , "Erato (anag.)" , "make speeches" , "Speak pompously and at length" , "Spout" .)