Give smack up during party with junkie at last (6)
I believe the answer is:
donate
'give smack' is the definition.
'donate' can be an answer for 'give' (donating is a kind of giving). I'm not certain of the 'smack' bit.
'up during party with junkie at last' is the wordplay.
'up' becomes 'nat' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'during' is an insertion indicator.
'party' becomes 'do' (do is a kind of party).
'with' is a charade indicator (letters next to each other).
'at last' says to take the final letters.
The last letter of 'junkie' is 'e'.
'do'+'e'='doe'
'nat' placed inside 'doe' is 'DONATE'.
Can you help me to learn more?
(Other definitions for donate that I've seen before include "give in kindness" , "Make a gift of" , "Make a contribution" , "Give to a charity or good cause" , "Give freely, maybe blood" .)