You will need ENJ to acquire JENJ, which can be done directly via the Enjin Wallet app.
It is not possible to purchase JENJ from exchanges. Enjin Coin (ENJ) can only be migrated to JumpNet (JENJ) via the Enjin Wallet.
To learn more about JENJ, please view this article.
I would like to convert my ENJ to JENJ, but I need to know where to buy ENJ first.
Enjin Coin is available on a wide variety of platforms and exchanges. You can view a select list of trusted exchanges here.
In order to migrate your ENJ over to JumpNet, you will need to send your ENJ to your Enjin Wallet address. This article explains on how to transfer ENJ to your wallet.
How can I convert my ENJ to JENJ?
You can convert your ENJ to JENJ by following this guide here.