There are more monoliths on this area, I will update the guide again soon when I have updated the main quest.
When you first arrive on the city, you will see an event about 2 tiger hellions fighting each other. The monolith is located nearby.
On the rightside (east) of the Ladylake Sanctuary (front entrance).
Go east after you have talked to Lailah about the Shepherd. If you missed it, it’s located on “Ladylake Outside the Aqueduct“.