Interact with the Zan'thik Resonating Crystal at the Whispering Stones in Zan'vess to incite Adjunct Sek'ot, then slay him.
On the southwestern corner of Zan'vess lie the Whispering Stones. Much like the towers here, they are critical in transmitting long-range sonic signals.
An adjunct of the Empress operates the stones, keeping her in communication with the Zan'thik forces. Disrupt the signal, then silence him.