Attribute quests are quests that grant you extra attribute points as reward. Every player should seek these out and complete them. You can only complete the Attribute quests from your homeland; for example, a Tyrian character cannot do the Factions or Nightfall quests.
There are only 2 Attribute Quests in each campaign, giving you 15 attribute points each:
The quests for Prophecies and Factions characters can be completed in any order, but because the quests in Nightfall are based on your rank in the Sunspear title, they must be completed in the order listed.