There are two types of certificates you can download for proof of completion:
The Organization Certificate includes list of all users who have completed the full OWASP Top 10 training plan as well as a date of completion. This will satisfy training requirements for PCI.
Click on the Certificate (PDF) button on the "Reports & Certificates" page to download the PDF.
Individual certificates can be download from the individual's profile page once they have completed the OWASP Top 10 training plan.