Scoffs (5)
(Other definitions for mocks that I've seen before include "Makes fun of" , "practice exams" , "Test examinations" , "trial examinations" , "Takes off" .)
'scoffs' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sneers that I've seen before include "Contemptuous or scornful remarks" , "Smiles contemptuously" , "Shows contempt by scornful expression" , "Expresses cynical contempt" , "Makes scornful remark, derides" .)