This is available in other questions that ive answered, but here:
Available Dialogues in Diablo 3 for Deckard Cain
Who Are You?
Available at the start of the quest: A Shattered Crown
Prophecy of the End Days
Available at the start of the quest: A Shattered Crown
Your Adopted Niece
Available at the start of the quest: A Shattered Crown
Mad King Leoric
Available at the start of the quest: A Shattered Crown
Disappears at the start of Sword of the Stranger
The Mysterious Stranger
Available at the start of the quest: Sword of the Stranger
Disappears at the start of the Broken Blade
*Not needed for conversation achievement.
The Archangel Tyrael
Available at the start of the quest: Sword of the Stranger
The Horadrim
Available at the start of the quest: The Broken Blade
Origins of the Coven
Available at the start of the quest: The Broken Blade
The Worldstone
Available after the end of the quest: The Broken Blade
Inaccessible at the start of The Doom of Wortham.
*NOTE: You can use the quest choose method to start at the beginning of Doom of Wortham, just don't talk to The Stranger, since when the quest officially starts, Deckard can't be talked to anymore.
Leah and Cain's Travels
Available after the end of the quest: The Broken Blade
Inaccessible at the start of The Doom of Wortham.
*NOTE: See above for details about the last 3 convos.
Taken from http://soe.hubpages.com/hub/Deckard-Cain-Lore-and-Character-Dialogue-Guide-Diablo-3