Almost mandatory somehow, to show how lottery numbers are drawn? (2,6)
I believe the answer is:
at random
'how lottery numbers are drawn?' is the definition.
'almost mandatory somehow' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'somehow' is an anagram indicator.
'mandatory' with its last letter removed is 'mandator'.
'mandator' is an anagram of 'AT RANDOM'.
'to show' is the link.
(Other definitions for at random that I've seen before include "without prior arrangement" , "Haphazard" , "Haphazardly" , "In no prearranged order" , "Without method or conscious decision" .)