The path of sn.exe could be change according to Visual studio version or windows version.
At my work computer i got at C:\Program Files\Microsoft SDKs\Windows\v7.0A\bin and
C:\Program Files\Microsoft SDKs\Windows\v7.0A\bin\NETFX 4.0 Tools\ directories
in windows XP operating system.
Then choose Tools / Get PublicKeyToken, and in the output window you will see something like the following:
the spaces from that value. Or, more recently, loading up Reflector and loading the assembly just to
get the public key token. Never even thought of this time saver, just using sn.exe from Visual Studio
as an external tool.