thanks for help Tartius and nora_lee.
I found the horn of star and first gem guidance of the sky.
I have got first clue from borcha and I cant find the river named wae.
@nora_lee I met ocuma but he left as me and my party hunted the remaining taiga bandits.
There are five clues altogether for a scoll, which teaches you a kind of special skill. You've got the first clue. Then you may get the other four:
clue 2 - horse market (it will appear around Khergit area, when you walk there with Borch and Marnid both in your troop)
clue 3 - Beat Hel to get it (mainline)
clue 4 - from Guy at Zendar (after the exercises and listening his stories)
clue 5 - check in a chest hidden in Jelkala town center.
Now you can go to look for the second gem according to the implication of Horn of Star.