You can get the selected cells values using the DataGrid.SelectedCells property and GetCellContent method of the DataGridColumn. For example:
for (int i = 0; i < this.datagrid.SelectedCells.Count; i++)
{
Console.WriteLine((this.datagrid.SelectedCells[i].Column.GetCellContent
(this.datagrid.SelectedCells[i].Item) as TextBlock).Text);
}
Hope this helps.