Is it permissible to study real human organs displayed on a screen during pathology lessons, while ignorant of their source and whether they belonged to a Muslim or a disbeliever?

What you have mentioned does not affect the permissibility of studying. Seeing parts of an assaulted corpse is not forbidden. This question is closer to obsessive thoughts and blameworthy over-elaboration. One must beware of extremism and excessive rigor in religion, for religion is ease, and those who are excessive have perished. Corrupt piety built upon conjecture and whims leads to more corruption than rectification.