Jew somehow has to know one welcoming extreme characters (9)
I believe the answer is:
ashkenazi
'jew' is the definition.
(I've seen this before)
'somehow has to know one welcoming extreme characters' is the wordplay.
'somehow' indicates anagramming the letters.
'to know' becomes 'ken' (I've seen this in another clue).
'one' becomes 'i' (Roman numeral).
'welcoming' is an insertion indicator (in sense of 'inviting in').
'extreme characters' becomes 'AZ' (letters at the extremes of the alphabet).
'ken'+'i'='keni'
'keni' going around 'az' is 'kenazi'.
'has' is an anagram of 'ash'.
'ash'+'kenazi'='ASHKENAZI'
(Other definitions for ashkenazi that I've seen before include "Northern Jew" , "Jew of eastern or central European descent" .)