[anrakushi]

There is now way to "know" how to pronounce all Japanese names by the characters you just become familiar with them. Family names are generally pretty good because you get to know them all and they are pretty straight forward like 田中(tanaka)、山田 (yamada)、岩田 (iwata), 森下 (morishita)、etc although some family names even some Japanese have trouble recognising, like my friend's 越智 (ochi) she has to tell many people how to say it.

first names are more difficult. there are common names such as 愛子 (aiko) that you can easily recognise but some parents give characters to their children and use a less common reading, making it hard to know when you read. i have a few friends who always have to respond to a different name from their real name because it is always being misread.

some online dictionaries have the more common names in their database and when you enter a name like 田中 it will tell you Tanaka, Japanese family name.