STAMP DUTY

My friend send a General Power of Attorney for looking after his property to his uncle from the USA duly attested by the Notary Public and Consulate now the attorney who is living in Laxmi Nagar Delhi and want to affixed stamp duty in the said Document, where he should go for that and what is the procedure for the same and/or is it mandatory for affixing stamp duty on the GPA in Delhi, please suggest.