You can get this by retrieving the property “DeclaringType”.
Quoting MSDN:
A Type object representing the enclosing type, if the current type is a nested type; or the generic type definition, if the current type is a type parameter of a generic type; or the type that declares the generic method, if the current type is a type parameter of a generic method; otherwise, null.
http://msdn.microsoft.com/en-us/library/system.type.declaringtype.aspx