Happiness of German fellow (4)
I believe the answer is:
'happiness' is the definition.
(glee is a kind of happiness)
'german fellow' is the wordplay.
'german' becomes 'g' (abbreviation).
'fellow' becomes 'lee' (I am not sure about this - if you are sure you should believe this answer much more).
'of' is the link.
Can you help me to learn more?
(Other definitions for glee that I've seen before include "Joy; part-song" , "Unrestrained joy" , "Impish enjoyment" , "Mirth - part-song" , "Old English part-song" .)