Tish gives you 5 scrying stones to get you started. You will probably need a lot more. They are purchased on the TS dock from Liets Rolyat or the Nektulos dock from Inaill Icoryk for 10s each. Five of them can also be given to you if you talk to Daria in Nektolus Forest by N'Mars Ascent ( -408, 2, -1262 ) /waypoint -408, 2, -1262.
Examine the stones near a "rainbow" effect on the ground to scry there. The rainbows are found randomly around a few specific POIs in multiple zones.
Occasionally you will win one or more Ancient Silver Coins as a reward. Other rewards include vendor items which you sell back to the scrying stone merchant, pieces of wearable armor, Training Tomes, or random undead to fight. Most of the rewards also give you the option of getting more scrying stones instead.
Note: You can purchase these from the broker to complete the task.