The buff provides +1% damage and healing each week, up to 15%.
A much smaller buff than the periodic +3% gained in Manaforge Omega, it's counterbalanced by stacking every week instead of every 3-4, ultimately providing the same +15% over time.
There is no reputation this time around, so all you need to do is speak to the NPC at the start of each raid instance to gain on the buff.
Each raid has its own separate buff, which can be gained by speaking to Riftblade Maella, En'liahn, and the Hurried Courier at the beginning of The Voidspire, The Dreamrift, and the March on Quel'Danas respectively.
