before we start to know how we can get the qualified name of the assembly, let’s define first assembly ”Assemblies are the building blocks of .NET Framework applications; they form the fundamental unit of deployment, version control, reuse, activation scoping, and security permissions. An assembly is a collection of types and resources that are built to work together and form a logical unit of functionality“ and assembly content

then let’s define Global Assembly Cache :“The global assembly cache stores assemblies specifically designated to be shared by several applications on the computer. Now, we can write code using reflection to can get the Fully Qualified Name of assembly”

public static void Main(){
        Type t = typeof(System.Data.DataSet);
        string s = t.Assembly.FullName.ToString();
        Console.WriteLine("The fully qualified name {0}.", s); }

My Source: http://msdn.microsoft.com/en-us/default.aspx