Going by the original module's text, divining shouldn't work.
The module claims "difficulty", and that such information is "often" fragmentary. It cites
legend lore as an example, which is fair enough. That spell should give fragments, anyway. But it certainly doesn't say that divination won't work at all.
In my players' case, they went above and beyond. They had read the story fragment in RttToH and realized they were dealing with something very scary. They were pretty banged up in the Necro College, and knew that even the necro's feared the tomb. Hence, they started with low order spells like
divination. I'm not sure if they cast
legend lore, but I gave them a fragment of a rhyme which alluded to some of the perils within in vague terms. Then they used
contact outer plane, made their insanity check, and tried to nail down a few more specifics.
Even after all that, all they knew (in vague terms) was that there was a terrible opponent against whom all their power was for naught, and who had never been defeated. So they used a
wish to learn of ways in which they could defeat him. And
even then, they only got some doggerel fragment ("...hard as bone and as inevitable as death... only blades of superlative sharpness in the hands of the most pure will avail, or the treasures of his own keeping in the hands of the depraved... etc, etc").
Side-note: Yeah, they had a ring of two wishes, courtesy of the remorhaz in G2. But that's far from the only wish-item available in 1e modules.
I guess that's the thing that disappoints me so much about Tomb of Horrors in general. Everybody expects the same outcome. The PCs survive = the DM failed. The PCs destroy the demi-lich = the players cheated. The only "acceptable" answer is the PCs fail in the mission, either TPKing in the tomb or running for their lives. That's just the mark of a poor module, in my books. I don't mind brutally hard, but I chafe at hearing the proper way to run a module is to ensure the party is screwed over.
I reckon the proper way to run Tomb of Horrors is to scare the heck out of the players, give them a slender chance of success, and let the dice fall where they may. If I'd thrown out all of their carefully-thought prep (and the
wish) just to preserve the module's rep as "unbeatable", they never would have progressed to the more interesting parts of RttToH... they would have learned the lesson that intelligence is worthless compared to the railroad... and they would have missed the experience of getting even more brutally scarred and tormented by Moil and the Fortress of Conclusion.
It still boggles my mind that they got through the Tomb of Horrors, though... but they failed to puzzle out the mystery in L2 - The Assassin's Knot. And they TPK'ed three times in Red Hand of Doom. And they TPK'ed in X1 - Isle of Dread. And they...