"Each empty equipment slot gives 20% Power and 20% Arcane. Does not count Vanity slots."
Acquisition
The Sovereignty Ring can be found in a Chest at [Aurealis Gateway] Azurite Cavern. (Map Link)
From the Bonsai, enter the cavern and make your way past the second Frost Golem to enter the main cavern area. Look for a broken down wooden tower near the edge and drop down to find the Chest.
Sovereignty Ring is not directly dropped by Enemies.