This is not about a method for successfully reading it, just me soliciting ideas on what could happen when you do.

I'll tell you mine first:
Scroll of omnipotence was written by Andor Drakon, as bait, to catch his latest victim and wannabe conquerer whilst unprepared.

Because he is such a chaotic being and understands chaos and law very well (perhaps he was once a champion of law that became progressively more corrupt with time), he foretold his own passing and fears the method by which he deicided his own predecessor. Also because of this understanding he knows what you'd fall for, or what you act like you would fall for in chasing power. So he sets up a red-herring, and like any chaotic being with a chaotic bias he gains the privilege of altering you any way he pleases and still has the power to do and whatever insight he still has on what applying such powers would actually do -- by making you drink (or not drink) your potions 'randomly' or randomly, with all their penalties and bonuses, same with your scrolls, same with your equipping and unequipping.

The results you ultimately get for reading the poison could be random at its easiest to implement, or be affected by actions taken in the game that Drakon remembers (or from a dev's perspective, what the game makes a record of), where it is able to recognise patterns in your habits. Basically he can seize control of your stats, your inventory, and/or your actions for a while (those options may be random, and whether they are can be conditionally random is random or not, etcetera), before allowing you to either enter the chaos gate (with your before-alteration corruptions and/or anything else that was changed -- or your after-alteration ones), or be teleported directly there if he feels impatient/confident/frightened instead. If ADOM were a modern-age Roguelike setting, he'd probably read, edit and/or vandalise a wikipedia article on your entire ancardian visit if not beyond that, and this gets to varying degrees reflected in what he ultimately does to you.

Basically i'm proposing an AI, literally, if even a somewhat basic one. I had an example of what kind of a pattern it might recognise and how it might go about doing it but I've forgotten it, as much as I had wanted to write that next, but one of the fundamentals of it would be that Drakon's stats are slightly altered when you take key actions in the game, and that impacts what he does after that to you, but his final choice, unless he has power over his choice, which may or may not be decided by anything, is always to have the scroll present you with the real success or error of throwing you into a lion pit and you'd better be the alpha lion.

Ah, now I remember what I was going to say: if you have a high learning score or have played very well -- preferably the second if the AI can be coded to do that -- Drakon knows (or for other reasons does not know) that you're very intelligent (in-game if you have high learning, IRL if something else about how you played) -- and think ahead by assuming you WOULD drop potions and -- he can't see you, but from that alone he forces you to drink up the potions on the floor as well because -- well, he's a God, duh. I.e. he's peerless in many understandings, including what a genius, average or stupid person's idea of an intelligent or more-intelligent-than-them being is and he's above all of that unless you have covered your bases (I'm just going to stick with dropping potions for now and leave it to others to think of more) very cleverly.

Apex success in the game is not reading the scroll successfully, but surviving the consequences afterward, and you get to know if you're smarter than the game's AI as well.