Which is the family name and which is the given name can be a problem even for other Chinese. Traditionally, the family name came first, but in places like Singapore and Hong Kong many Chinese have adopted the western custom of given name first, family name second.
To be polite, and get around any confusion, they'd address your man as ''Mr Tran'', just as, if your name were John Smith, they'll address you as ''Mr John''.
The only way to be sure is to actually ask the person!