Ni No Kuni II will be receiving three DLC, the first being a free Adventure Pack that is currently scheduled for release on August 9th. The pack will contain new bosses and quests and some extra floors in the Faraway Forest. You can probably also expect more loot and new quests
We know next to nothing about the other two DLC. One will be coming in "Winter 2018" and the other story pack will arrive in early 2019.
Each of the DLC are part of the Ni No Kuni II season pass.