Is there any way that I can cast unknown object into generic list to get list of items from object by given ProperyName.
Object can be any generic list like List<Country>, List<Area> or List<Region> but I need to get data by given displayMember.
For Example:
List<City> listCities = new List<City>(); //Cities data with (CityID, CityName)
object dataSource = listCities;
string displayMember = "CityName";
string valueMember = "CityID";
How to get List of CityName from dataSource object of object type?

You'd have to use reflection, basically. For example:
// This assumes it really is just a List<T>...
IEnumerable list = (IEnumerable) dataSource;
Type elementType = list.GetType().GetGenericArguments()[0];
PropertyInfo property = elementType.GetProperty(displayMember);
List<object> displayValues = list.Cast<object>()
.Select(v => property.GetValue(v, null))
.ToList();
(You'd want to add a bunch of error checking - for example, that property isn't null...)
See more on this question at Stackoverflow