Modifying a data table of report data
is there any possibility of optimizing the above code


Eliminating unnecessary processing will help...

Remove Needless if

if (!row.IsNull(col))
{
    b_dataValue = true;
    if (b_dataValue)
    {
        // ...
    }
    else
    {
        dt.Rows.Remove(row);
    }
}


b_dataValue is always true, so the if is not necessary, and the else will never execute. So ...

if (!row.IsNull(col))
{
    b_dataValue = true;
    {
        // ...
    }
}


Move If's to the top

If the table is null or has no columns then there's no point in going on. So check for this up front. This removes 2 nesting levels.

private void ModifyDataTable(DataTable dt) {
    if (dt == null) return;
    if (dt.Columns.Count &lt;= 0) return;
    // ...
}


Reference by Table Name and Remove more If-ing

I'm guessing that your code is handling at least 2 different tables. If this is true then based on the name call "thisTable" code or "thatTable" code. Then you can eliminate all that checking for column names because you know they are there. And it eliminates another layer of if

private void ModifyDataTable(DataTable dt) {
    if (dt == null) return;
    if (dt.Columns.Count &lt;= 0) return;
    if (dt.TableName == "thisTable") DoThisTableStuff(dt);
    if (dt.TableName == "thatTable") DoThatTableStuff(dt);

    // Knowing what table we're dealing with, code like this
   if (col.ColumnName == "report_data0") row[col] = rowreport_data0Sum + "%";
   else if (col.ColumnName == "report_data1") row[col] = rowreport_data1Sum + "%";

   // could turn into this
   row["report_data0"] = rowreport_data0Sum + "%";
   row["report_data1"] = rowreport_data1Sum + "%";

}