Is it common knowledge that starships go through the warp and that daemons live there? Do they know about the Gellar field?
Do an average citizen know about rebellions, heretic/chaos cults and aliens? By that, I don't mean what the various cults do or their agendas but rather that they exist at all - and that Chaos and Chaos gods exist. Or are they just taught that everything non-imperial/non-sanctioned is evil and therefore should be destroyed/reported? How much info trickle back from war zones - can average humans separate an eldar from an ork and judge the threats accordingly or are both just aliens to be feared, loathed and killed?
How much do normal citizens know about the Horus Heresy and its outcome? Is it known at all that several legions turned to Chaos, or are the Adeptus Astartes portrayed as divine, pure, impeccable warrior-angels? Is "fallen Space Marine" even a known concept? Would an imperial citizen be able to identify a Chaos marine as a foe (well, some are pretty obviously monsters, like Death Guard)? I mean, Iron Warrior, Alpha Legion and Thousand Sons tend to have few or no obvious mutations and little Chaos iconography, right? With the virtue of ignorance, would normal people even recognize Chaos symbols or regard them as non-imperial? Death symbols exist in abundance in the Empire as well and strange implants/gear/weapons seem not umcommon.
Do normal people even know that the Emperor was alive once, or is it basically "Your God-Emperor watches over you from His Golden Throne on Holy Terra with his mighty, all-seeing eyes like He ALWAYS has"?
I ask, because I feel I get mixed information about it from the various 40K sources. Everything seems to be shrouded in mystery for the acolytes. Not even Adepts get to know Scholastic Lore: Archaic - and they are the loremasters! Only Imperial psykers and Tech-priests get history lessons, for some reason.