It's pretty straightforward:
int itemRow = Grid.GetRow(myTileViewItem);
int itemColumn = Grid.GetColumn(myTileViewItem);
Note that you should use the above methods with RadTileViewItem objects. In case you are data binding the TileView, you can get a reference to the dynamically created RadTileViewItem containers that will wrap the business objects from your data source by using the ItemContainerGenerator:
RadTileViewItem container = myTileView.ItemContainerGenerator.ContainerFromItem(myBusinessObject) as RadTileViewItem;
Keep in mind that the ItemContainerGenerator will return the containers only after they have been created, i.e. the TileView has actually been rendered on the screen.
Let me know if the above info helps.
the Telerik team