Hello Aspirant,
You can get the EWS certificate from your local government authority or Tehsildar. The certificate is called an 'Income and Assets Certificate', and this is the proof that is required to avail the EWS reservation.
After seeing your documents, the official will give you your EWS reservation certificate.
Hope that helps.
Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile