It depends how it`s pronounced. Jee? Chee? Zee? Shee?
The Chinese name Xi, is written "シー" in katakana. For example Xi Jinping is シー・チンピン, though it's more common for Japanese people to use their usual kanji readings for Chinese characters, which gives しゅう きんぺい in this case. (I think pronunciation conventions may be shifting slowly though).
http://ja.wikipedia.org/wiki/%E7%BF%92%E8%BF%91%E5%B9%B3
If you're not thinking of the Chinese name, then you need to give some more information.
It looks like you're new here. If you want to get involved, click one of these buttons!