In order to locate where a .NET executable has been loaded from, you can simply write:

var assembly = System.Reflection.Assembly.GetExecutingAssembly ();
var dir      = System.IO.Path.GetDirectoryName (assembly.Location);

This will return the path of the containing folder, not a file:// URI as you would get back by using .CodeBase instead of .Location (see this Stack Overflow question on the topic).