Per Alan's keynote at PW 2018, the PDC service is free for ALL pega customers. Feel free to contact your account manager if you need confirmation.
All customers should have a PDC tenant ready and waiting. There is no enrollment / entitlement process. If you are an authorized support contact with rights to create / update support tickets, you can access PDC from the link in https://community.pega.com/support (next to the link for managing support tickets)
Ideally, to use PDC you just need to log in from browser, read the instructions on the welcome page, click to copy your unique service integration URL to clipboard, then go to your system, navigate to system / settings / PDC and paste the URL
In reality, servers running in on-premise data center may not have access to send data to PDC via public internet so you will have to configure your system / network with an appropriate gateway or proxy. Proxy and network setup is done outside of Pega and will be specific to your actual data center policies and preferences.
Feel free to post questions tagged with 'predictive diagnostic cloud' or to reach out to pega support to forward questions to the PDC team ..