[RPG] What skill should PCs use to find information in books in D&D 3.5e

Use a Wisdom check.

Ability Checks

Sometimes a character tries to do something to which no specific skill really applies. In these cases, you make an ability check. An ability check is a roll of 1d20 plus the appropriate ability modifier. Essentially, you’re making an untrained skill check.

Well, there’s the really simple answer of be an elan, which are immortal psionic creatures. Humans can theoretically become elans, though the process is deliberately left undescribed and up to the DM, plus it costs you all class levels, skills, feats, and so on (you start over as a 1st-level character).

Besides that, the psionic-magic item-creation transparency rules from Magic Item Compendium pg. 232 means that the regular lich template is probably available to humanoid psionic characters. The only requirement for becoming a lich is to be humanoid, and to be capable of crafting a phylactery, and a psionic character can craft psionic versions of magic items by doing the following:

• Substitute Craft Universal Item for Craft Wondrous Item.
• Substitute manifester level for caster level.
• Substitute “a psionic power of similar flavor” to craft an item that “includes a spell prerequisite, but the effect of the item does not directly implement the spell.” This seems like it should be more than sufficient to substitute “ability to manifest powers” for “ability to cast spells,” but it doesn’t come out and say that.

Interestingly, this is true even if playing with the “psionics is different” variant; Magic Item Compendium specifies that in that case, the item created this way is specifically psionic, but you can still do it.

Just for completeness’s sake, the extremely well-received third-party book Hyperconscious by Bruce Cordell (one of the primary authors of the Expanded Psionics Handbook) had a specific psionic lich adaptation.

But if you don’t buy that, don’t use that rule, or are not humanoid, there are other options.

The spectral savant from Complete Psionics is kind of mid-way between a lich or a vampire, and results in immortality. The grim psion even gets a kind of phylactery, though it is a 3.0 class that will require some adaptation. The psion uncarnate doesn’t actually say that you become immortal, but it’s kind of weird to imagine “a being of pure psionic consciousness” aging.

And then, just about any high-level psion can easily make a phylactery of sorts, though it does result in level-loss when you die, while a phylactery doesn’t.