How do I know which tax treaty applies?

You need to determine in which country you are considered a tax resident and in which country the issuer is a tax resident. For instance, if an Irish tax resident receives a dividend payment on his/her shares of Volkswagen AG (Germany), the Irish-German tax treaty needs to be consulted. It is not relevant that DEGIRO is a tax resident in the Netherlands for the application of the tax treaty, as DEGIRO is not the ‘beneficial owner’ of the income.