Discover tragic king has end in prison (5)
I believe the answer is:
learn
'discover' is the definition.
(I know that discover can be written as learn)
'tragic king has end in prison' is the wordplay.
'tragic king' becomes 'Lear' (Shakespeare's King Lear).
'has' means one lot of letters go next to another.
'end in' suggests the final letters.
The final letter of 'prison' is 'n'.
'lear'+'n'='LEARN'
(Other definitions for learn that I've seen before include "Acquire 28 across" , "be taught a lesson" , "Study - find out" , "Find out - assimilate facts" , "Absorb as knowledge, from book or experience" .)