1st select the 1st row details from gridview den use for loop to insert the into new table with additional information.
for(int i=0;i<gridview1.rows.count;i++)>
{
string staff_name = GridView1.Rows[i].Cells[1].Text;
string staff_dept = GridView1.Rows[i].Cells[2].Text;
string str = "insert into intrmarks(VTUNO,ROLLNO,NAME,DEPARTMENT,SEM,IA1,IA2,IA3,FINAL_MARKS,mobile,email,Staff_Name,SUBJECT_NAME)values('" + txtvtu.Text + "','" + Convert.ToInt32(txtrno.Text) + "','" + txtsname.Text + "','" + ddldes.Text + "','" + Convert.ToInt32(ddlsem.Text) + "',0,0,0,0,'" + txtmob.Text + "','" + txteml.Text + "','"+staff_name+"','"+staff_dept+"')";
SqlCommand strCmd = new SqlCommand(str, con);
strCmd.ExecuteNonQuery();
}