How can i bind DataTabe to GridView in C#

It may vary depending upon the DataSource of your GridView.
Try:

//If DataSource of GridView1 is a DataTable
DataTable dt = (DataTable)GridView1.DataSource;

//If DataSource of GridView1 is a DataView
DataView dv = (DataView)GridView1.DataSource; 

If you want to make some changes while porting the data, you have to loop through. But, you cannot convert GridViewRow to DataRow. You have to manually create columns first, then loop through all the rows. Within this loop, you would need to loop through all the columns of the row and copy it to the DataRow that you are creating.

//This is just a Psuedocode
DataTable dt = new DataTable();
//Add columns here
dt.Columns.Add(); //or something similar
//go on till all the columns are added
//loop and second loop
foreach(GridViewRow gvr in GridView1.Rows)
{
   DataRow dr = dt.NewRow();
   
   //second loop - looping all columns
   for(int i = 0; i < gvr.Rows.Count; ++i)
   {
      dr[i] = gvr.Cells[i].Text;
   }
}