To obtain the 20% senior discount in the Philippines, start by securing your Senior Citizen ID from your local government office. Once you have your ID, present it at participating establishments, such as restaurants, grocery stores, and hotels. Ensure to ask for the discount before finalising your purchase, as it should be applied at the point of sale. Additionally, check with the establishment to confirm they accept senior discounts. For detailed information and potential updates, visiting the official government website can be beneficial.