Need to debug my Web API service that's requested from a client machine - need help, how do I do this?

Attach to process - http://msdn.microsoft.com/en-us/library/vstudio/3s68z0b3.aspx

Make sure "Show processes from all users" is checked, and pick w3wp.exe

You may need to hit the service once first to make sure its started.

To debug an app that's hosted by IIS, you want to attach to process (in Visual Studio it's Tools->Attach to Process or Ctrl+Alt+P) and pick w3wp.exe from the list (you might have to check a few boxes for the process to show up).