正确的更新命令 [ ^ ]是：

  UPDATE  TableName  SET  FieldName = Something 
 WHERE  AnotherFieldName = criteria 

听起来像是要插入数据。如果是，则替换 UPDATE with

  INSERT   INTO  TableName（< FieldList>）
 VALUES （< Values>）

protected void Button_update_Click(object sender, EventArgs e)
        {
            conn.Open();
            string updateQuery = "update emp_details(emp_name,father_name,age,sex,dob,nationality,state,city,mobile_no,exp,qual,emp_sal,email) values(@name,@fname,@age,@sex,@dob,@nation,@state,@city,@mob,@exp,@qual,@sal,@email) ";
            SqlCommand com = new SqlCommand(updateQuery, conn);

            com.Parameters.AddWithValue("@name", TextBox_emp_name.Text);
            com.Parameters.AddWithValue("fname", TextBox_father_name.Text);
            com.Parameters.AddWithValue("@age", TextBox_Age.Text);
            com.Parameters.AddWithValue("@sex", RadioButtonList_sex.Text);// is this NOTATAION correct of selecting Dropdownlist
            com.Parameters.AddWithValue("@dob", TextBox_dob.Text);
            com.Parameters.AddWithValue("@nation", TextBox_nationality.Text);
            com.Parameters.AddWithValue("@state", TextBox_state.Text);
            com.Parameters.AddWithValue("@city", TextBox_city.Text);
            com.Parameters.AddWithValue("@mob", TextBox_mob.Text);
            com.Parameters.AddWithValue("@exp", DropDownList_exp.Text);
            com.Parameters.AddWithValue("@qual", DropDownList_qual.Text);
            com.Parameters.AddWithValue("@sal", TextBox_sal.Text);
            com.Parameters.AddWithValue("@email", TextBox_email.Text);
            com.ExecuteNonQuery();
            conn.Close();---------------->here it is showing an error"incorrect syntax near'(' "
            Response.Write("Updation Succesfull");
        }

The proper update command[^] is:

UPDATE TableName SET FieldName = Something
WHERE AnotherFieldName = criteria

Sounds like you want to insert data. If yes, then replace UPDATE with

INSERT INTO TableName (<FieldList>)
VALUES(<Values>)