Try again to practise with last two missing (6)
I believe the answer is:
rehear
'try again' is the definition.
('hear' can be a synonym for 'try' so perhaps 'rehear' is OK for 'try again')
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for rehear that I've seen before include "Retry (a lawsuit)" , "Try again (in court)" , "Hold the trial again." , "be a sympathetic listener, not for the first time" .)