Tactful jerk is after a qualification (10)
I believe the answer is:
diplomatic
'tactful' is the definition.
(similar in meaning)
'jerk is after a qualification' is the wordplay.
'jerk' becomes 'tic' (jerking movement by the body).
'is after' means one lot of letters go next to another.
'a qualification' becomes 'diploma' (type of academic qualification).
'tic' after 'diploma' is 'DIPLOMATIC'.
(Other definitions for diplomatic that I've seen before include "Discreet" , "Tactful" .)