What are the duties of a son toward his well-off father who did not spend on him in his childhood, and is now demanding money from him while the son is in need and has children, considering that the father does not ask about him?

Your duty towards your father is to honor him and treat him kindly to the best of your ability. This requires abstaining from anything that might harm him, because honoring parents is an obligation that does not cease due to their shortcomings towards their children. However, if your father asks for your money while he is not in need of it and you are, you are not obligated to give it to him, and this would not be considered disobedience.