I want to implement Unicode Normalization in C++, specially NFKC. To do so I need some reference source code in any language(prefarable C++).
Or you may suggest me how can I start my implementation.
You're in luck, because a regular at the Lounge<C++>
here at SO.com is writing a complete Unicode implementation in C++. It is meant as a full replacement of ICU, without any of its drawbacks:
https://bitbucket.org/martinhofernandes/ogonek/
It doesn't currently implement NFKC, but NFC and NFD are implemented, and could be used as "some reference source code".