http://msdn.microsoft.com/en-us/library/b0bktkzs.aspx says:
Examine the build log in the intermediate files directory to see what actually executed. The path and name of the build log is represented by the MSBuild macro expression, $(IntDir)\$(MSBuildProjectName).log.
[And the easiest way to get there is to do Project|Show all files, then go to Solution Explorer and right click to Open Folder in Windows Explorer]
EDIT: To appease our disgruntled -1er... You could obviously infer from this that you could add a <Execute Command="notepad.exe $(IntDir)\$(MSBuildProjectName).log"/> or similar if it needs to literally pop up, but that doesnt make sense to me.
EDIT 2: EXAMPLE. Edit the .csproj file, and in the section with
<!-- To modify your build process, add your task inside one of the targets below and uncomment it.
Other similar extension points exist, see Microsoft.Common.targets.
-->
Change it to:
<Target Name="AfterBuild">
<Exec Command="notepad.exe $(IntDir)\$(MSBuildProjectName).log" />
</Target>
Reason I didnt expand it out is that this would get annoying quick. YOu could potentially put:
notepad.exe $(IntDir)\$(MSBuildProjectName).log
In your Post Build step. This would work slightly better as it would only fire when the compile has actually done something.
BTW highly recommend getting the Hashimi book - it makes all this stuff obvious and makes you give answers that assume its straightforward :P