Hello Anshu,
The application forms for Delhi University Joint Admission Test have not yet been released by the University . DU JAT 2019 Application Form will be available online at www.du.ac.in.
This is official website of DU and official notifications will first be released here only, so be in touch with it to be updated.
You will have to register yourself at the Delhi University Undergraduate Admission Portal to be able to sit for DU JAT 2019. The basic eligibility is that you must have passed class 12th with 60% marks in aggregate.

All the best! :)