What should one do with a father who asks for money to spend without disclosing where it will be spent, refuses to discuss it, and is not truthful when confronted?

Filial piety is a religious obligation, and obeying one's father in what is good is a path to Allah's pleasure. As for what the father takes from money: if it is for the need of sustenance and he is unable to earn, then it is obligatory upon you [to provide it]; otherwise, it is preferable not to deprive him of it, as an exaggeration in showing kindness to him.