According to Hunter Wikia:
Leaving the last sentence aside, her full name is Biscuit. Basically:Biscuit Krueger (ビスケット=クルーガー, Bisuketto Kurūgā) is a professional Treasure Hunter that enlisted in clearing the video game Greed Island following the auction for the game in Yorknew City. She prefers to be called "Bisky."
1) If you believe her full name should be written in romanji, then it's Bisuketto.. and her corresponding nickname would be Bisuke.
2) If you believe her full name should be Anglicised as Biscuit, then her corresponding nickname would be Bisky.
I'm in the latter camp, just as I prefer Shadow Clone Technique to Kagebunshin no Jutsu in my subs. It's not an absolute standard, since I do prefer Onii-chan to Brother (because "Brother" has a religious order feel in my head), but names have a proper meaning or form, I'd like that to be conveyed.
If it's not Isuzu-chan Mii~