How do I find the PublicKeyToken for a particular dll?

I need to recreate a provider in my web.config file that looks something like this:

<membership defaultProvider="AspNetSqlMemProvider">
  <providers>
    <clear/>
    <add connectionStringName="TRAQDBConnectionString" applicationName="TRAQ" minRequiredPasswordLength="7" minRequiredNonalphanumericCharacters="0"
         name="AspNetSqlMemProvider"
         type="System.Web.Security.SqlMembershipProvider, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"
    />
  </providers>
</membership>

However, I get a runtime error saying this assembly cannot be loaded, and I think it is because I have the wrong PublicKeyToken. How do I look up the PublicKeyToken for my assembly?

Alternatively, am I going entirely the wrong way with this?

Using PowerShell, you can execute this statement:

([system.reflection.assembly]::loadfile("C:\..\Full_Path\..\MyDLL.dll")).FullName

The output will provide the Version, Culture and PublicKeyToken as shown below:

MyDLL, Version=1.0.0.0, Culture=neutral, PublicKeyToken=669e0ddf0bb1aa2a

Using sn.exe utility:

sn -T YourAssembly.dll

or loading the assembly in Reflector.

If you have the DLL added to your project, you can open the csproj file and see the Reference tag.

Example:

<Reference Include="System.Web.Mvc, Version=3.0.0.1, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL" />

sn -T <assembly> in Visual Studio command line. If an assembly is installed in the global assembly cache, it's easier to go to C:\Windows\assembly and find it in the list of GAC assemblies.

On your specific case, you might be mixing type full name with assembly reference, you might want to take a look at MSDN.