Loop thru Gridview

DataTable dt = sQLUtility.GeBookPlanningRecommendation(HRpl, BookCollection, StudentCollection).Tables[0];
if (dt != null)
{
DataColumn Remarks = new DataColumn("Remarks", typeof(string));
dt.Columns.Add(Remarks);
DataColumn Dates = new DataColumn("Date", typeof(DateTime));
dt.Columns.Add(Dates);

grdPlanning.DataSource = dt;
grdPlanning.DataBind();

DataTable selectedRows = dt.Clone(); // create a new DataTable with the same schema as dt
foreach (GridViewRow row in grdPlanning.Rows)
{
    // check if the "Date" column has a value
    DateTime date;
    if (DateTime.TryParse(row.Cells[2].Text, out date))
    {
        DataRow newRow = selectedRows.NewRow();
        newRow["Column1"] = row.Cells[0].Text; // replace "Column1" with the name of your first column
        newRow["Column2"] = row.Cells[1].Text; // replace "Column2" with the name of your second column
        newRow["Remarks"] = row.Cells[3].Text; // replace "Remarks" with the name of your "Remarks" column
        newRow["Date"] = date;
        selectedRows.Rows.Add(newRow);
    }
}

// selectedRows DataTable now contains only the rows that have a value in the "Date" column
// you can use this DataTable for further processing
}

The code you provided is creating a DataTable `dt` using data returned from a function `GeBookPlanningRecommendation`. The DataTable `dt` is then used as a data source for a GridView `grdPlanning`, which is then bound to display the data. The DataTable `dt` is created with two additional columns, "Remarks" and "Date". The "Remarks" column is of type string, and the "Date" column is of type DateTime. The "Date" column is editable in the GridView. You want to get the rows from the GridView that have values in the "Date" column and add those rows to the DataTable `dt`. To do this, you need to loop through the GridView rows, check if the "Date" column has a value, and if so, add the row to the DataTable `dt`. You can do this by adding the following code after the GridView is bound: 

foreach (GridViewRow row in grdPlanning.Rows)
{
    DateTime date;
    if (DateTime.TryParse(row.Cells[1].Text, out date))
    {
        DataRow newRow = dt.NewRow();
        newRow["Remarks"] = row.Cells[0].Text;
        newRow["Date"] = date;
        dt.Rows.Add(newRow);
    }
}

This code loops through each row in the GridView, tries to parse the value in the second cell (the "Date" column) to a DateTime object, and if successful, creates a new DataRow for the DataTable `dt` and adds the "Remarks" and "Date" values from the GridView row to the new DataRow. The new DataRow is then added to the DataTable `dt`.