Note the German king who made a disastrous wish (5)
I believe the answer is:
midas
'king who made a disastrous wish' is the definition.
'midas' can be an answer for 'king' (mythical king). I am not certain of the rest of the definition.
'note the german' is the wordplay.
'note' becomes 'mi' (as in 'do re mi').
'the german' becomes 'das' ('the' in German).
'mi'+'das'='MIDAS'
Can you help me to learn more?
(Other definitions for midas that I've seen before include "His touch made gold" , "Mythical king who had the power to turn everything to gold" , "Legendary king whose touch turned things to gold" , "I'm sad (anag) -- king of Phrygia" , "Greek mythological king with money-making touch" .)