One of the Kardashians upset over a party for emperor (6)
I believe the answer is:
mikado
'for emperor' is the definition.
(mikado is a kind of emperor)
'one of the kardashians upset over a party' is the wordplay.
'one of the kardashians' becomes 'kim' (I've seen this in another clue).
'upset over' says the letters should be written backwards (knocked over).
'party' becomes 'do' (do can informally mean a party).
'kim' backwards is 'mik'.
'mik'+'a'+'do'='MIKADO'
(Other definitions for mikado that I've seen before include "Japanese emperor, operetta and delicious biscuit" , "Japanese emperor's title" , "G & S' alternative for "The Town of Titipu"" , "mperor" , "Musical emperor of Japan" .)