I already done with this Kayelinth farm,..in walkthrough...talk to jailyn..but nothing happen...did I miss something?

Do you have a scene with both kayetlin and jaylin in beach island? It probably should be before quest

You dont need a completed scene on the beach with Jaylin and Kay  for this quest.

You need to have a conversation with WindSpirit first.
If you completed all main quests, she will stay in garden of your castle on the left side where maid Flora taking care of flowers. Then she will invite you for a private talk in Ebron village. After that you can go to Jaylin in treasure room to start quest for dragon shape.