What is the ruling on reading the cup when the one who does so knows of its prohibition? And is this considered a type of polytheism (shirk)?

We advise you to supplicate for your grandmother and mother and to let them listen to tapes of scholars teaching Tawhid (definition) (monotheism) and warning against Shirk (definition) (polytheism) and the actions of soothsayers and diviners. Encourage them to supplicate and seek help through prayer to fulfill their needs, and to stay away from forbidden means. Remind them that obedience to Allah is a cause for achieving benefits in both worlds, and that sins are a cause for deprivation. To review the prohibition of the actions of soothsayers and diviners, approaching them, and believing them, you can refer to the following fatwas: 63778, 62538, 64890, 32356, 40711, and 32151.