How to read this word 鑫?

鑫---[音]
商店字號，人名常用的字，
取其金多興旺的意思。

If you mean how to pronounce this work, please refer to this link
http://hk.dictionary.yahoo.com/search.html?q=1&s=%F8%CA&Submit=+%ACd%A6r+
xin
ㄒㄧㄣ

1.a word of no definite meaning, used only in names, with a connotation of prosperity or good profit

讀　”音”