You'll need to collect the 14 Heroic Saga artifact collectibles scattered throughout Svartalfheim to unlock all 14 Boasts to tell Kara. Kara's Domain is unlocked after collecting your first Heroic Saga. The Tales you can tell Kara are based on your progress through the base game and DLCs. Kara also offers her own Tale; however, you cannot change the boasts of her tale. The earliest you can do this is after collecting 4 Heroic Sagas. Return to Kara and choose a Tale (preferable a low difficulty one) and then select a combination of 4 boasts to add to it. Complete the Tale by defeating the enemies.