Rakanoth's Wake is a Unique Boots in Diablo IV Season 15 for All classes. It comes from General Unique Pool - every Lair Boss (Initiate, Greater, Exalted, Belial) can drop it in addition to their dedicated table (one guide's Boss Loot Table Cheat Sheet).
Unique power
When you cast a Skill with a Cooldown, you explode, dealing [450 - 525] Fire damage.
Affixes
Primary Core Stat
All Damage Multiplier
Where it drops
General Unique Pool - every Lair Boss (Initiate, Greater, Exalted, Belial) can drop it in addition to their dedicated table (one guide's Boss Loot Table Cheat Sheet)