even if you havnt been turned into a heartless and made a smart Nobody, you can easily find out your Org. XIII name! Just take your REAL first name and make an anagram of it ( one word made out of letters from a different word) and also put a X in there some where, ( EX: Sora = Roxas)
since my real name is Conner my Org. XIII name would be , and this is hard to pronounce, Ronxnec
try to use your imagination and have fun!