Go through and knock the top off pudding (5)
I believe the answer is:
rifle
'go through' is the definition.
(I've seen this in another clue)
'top off pudding' is the wordplay.
'top off' means to remove the first letter.
'pudding' becomes 'trifle' (type of pudding).
'trifle' with its initial letter taken off is 'RIFLE'.
'and knock the' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for rifle that I've seen before include "An arm" , "Gun - ransack" , "Gun; sack" , "Search with intent to steal" , "Gun - steal" .)