All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
As for your father's income, its unlawful part is what was taken from bribe or other illegal means. As for what was in return for his work, it is lawful, provided that his work itself is lawful. There is no effect of the prohibited bribes he takes on the lawfulness of the remaining part of his income.
As regards your educational expenses, if your father spent on you from his mixed money (i.e. lawful money mixed with unlawful money), not from the unlawful part only, then there is no harm in accepting it. But if he used to spend on you from what you know to be from pure bribery, then you should not have taken it. However, it is incumbent upon you to make a sincere repentance about the past and be careful regarding the future and not take from him except what you know to be lawful.
With regard to your certificate that you got or will get, there is nothing wrong with working with it in whatever field you wish for the prohibition has nothing to do with it. The sin is related to the person who took it, and not to the certificate itself. Sincere repentance is its expiation as we have previously explained. For more benefit, please refer to Fatwa 102369.
It is worth noting that it is not permissible for you to neglect the matter of giving advice to your father as long as you are able to do so and it will cause you no harm. So, try to be very kind to him and take the initiative to remind and advise him, perhaps Allaah The Almighty will guide him at your hands.
Allaah Knows best.