when addressing a Japanese man in business, Which name does the -san go behind his surname or his given name?
In business you should speak more formally. You should refer to a person by their family name. If you use their given name for any reason, you should use their full name. For example:
Your business acquaintance has the family name "Saito" and the given name "Kenji". In conversation, you should call him "Saito-san". If you need to call him Kenji, you should call him "Saito Kenji-san".
Never use "-san" after your own name.