Now possible to get through the Oasis event. Choose either "[Oasis] Facing Saunil Siege Captain" or "[Oasis Quest] Secret Behind the Treant Timber" from the black spirit. When you complete the quest you get knowledge. If you want to get S knowledge you have to delete the knowledge & try again the next day. Keep in mind that you probably want to keep the knowledge when the event ends. Since we don't know if we can get it again afterwards.

Can be Obtained by talking to Valks In Calpheon after completing quest "[Boss] Saunil Siege Captain"