Head to Vunkerl Inlet (S). You're looking for a ??? on the north side of the bridge in (H-6). Examine the ??? for a cutcene. You will receive the Vunkerl Herb Memo at the end of this cutscene.
Acquire the Vunkerl Herb by examining the Leafy Patch on the shore of the lake in (F-5).
You need to get the proper herb color according to the time of day that you arrive at the Leafy Patch.
If 00:00~07:59 pick red.
If 08:00~15:59 pick blue.
If 16:00~23:59 pick green.
Upon examining the Leafy Patch, you will have a choice of which color herb to pick.
Early morning is red, afternoon and late morning are blue, and evening and late afternoon are green.
It does not matter when you hand in the herb, as long as it was harvested at the proper time.
After you get the herb, return to the ??? at (H-6) for the final cutscene and the reward of a Carbon Fishing Rod.