Well, here is how I broke down the knowledge skills:
Arcana- used to ID spell effects, magic item ID, detect magic
Dungeoneering- used like Nature indoors, tracking underground, ID subterranean plants and animals, knowing about geology, underground foraging, etc
Nature- used for tracking, ID plants and animals, herbalism, foraging
Religion- used to know about your religion (+3 bonus) or other religions and their teachings, theology, symbolism, prophecies, etc
and the new ones:
Elemental Lore- recall info about elemenal creatures, including demons, and how the elemental planes react, elemental lore
Faerie Lore- used to recall fey legends, Feywild lore, events, creatures, and misc lore
Forbidden Lore- used to recall info about the Far Realm and its denizens (abberations)
Spirit Lore- used to recall info about the Shadowfell, spirit creatures who dwell there, etc
Supernal Lore- gives info about devils, angels, the gods, Astral Sea, etc
Undead Lore- used to ID undead, know common legends about the undead, and signs of undead activity
The classes that get these as class skills are:
Cleric: Arcana, Religion, Spirit Lore, Supernal Lore, Undead Lore
Fighter: None
Paladin: Religion, Supernal Lore
Ranger: Dungeoneering, Nature
Rogue: Dungeoneering
Warlock: Arcana, Religion and Faerie Lore, Forbidden Lore, or Supernal Lore- depending on type of pact
Warlord: None
Wizard: Arcana, Elemental Lore, Faerie Lore, Religion, Forbiddern Lore, Spirit Lore, Supernal Lore, Undead Lore