John Wants His Employees to Be Aware That They Should

Short Answer

John wants his employees to be aware that they should act ethically. He should
fire anyone who behaves unethically.
not draw public attention to any employee's unethical behaviour, but instead deal with it privately.
publicly reward ethical behaviour and ignore unethical behaviour.
publicly discipline employees who behave unethically, but don't fire them.
adopt a written code of ethics.