Question

how to prepare 0.02 n edta​

Answer 1

Well, CTAB buffer will require very small amounts of 0,02M EDTA in final solution so preparing 1 litre will be so high, it will also have a short expire date after preparation.

I suggest you to prepare 54 ml with 0,2 mg EDTA (but you should check your owns moelcular weight, I used 292g/mol) than add half of a NaOH tablet or KOH.