You need to pass the value of the date to the parameter
protected void Button1_Click(object sender, EventArgs e)
{
SqlConnection sqlcon = new SqlConnection(ConfigurationManager.ConnectionStrings["MyDatabase1ConnectionString"].ToString());
sqlcon.Open();
string query = "select * from Ticket where date = @Date";
SqlCommand cmd = new SqlCommand(query, sqlcon);
SqlParameter date = cmd.Parameters.Add("@Date", "date value here");
SqlDataReader rdr = cmd.ExecuteReader();
GridView1.DataSource = rdr;
GridView1.DataBind();
sqlcon.Close();
}
}