Unfortunately it is not possible to get this value if you have forgotten it.
The certificate password it is baked into the application during the install and is not accessible, and even if it was, it is encrypted and cannot be converted to plain text.
On the certificate password screen is where you enter a password that will be used for controlling access to keys used for encrypted passwords and data.
This password is required when installing any other Orchestrators or cluster nodes to existing Orchestrators.
If you forget this password, you will be required to rerun this installation process again to reset this password.
Please keep a record of the CA Process Automation certificate password.
From the installation guide:
Install the Domain Orchestrator - CA Process Automation - 04.3.02 - CA Technologies Documentation
10.Type a certificate password, type it again, and then click Next.
In the Set Certificate Password page, before you click Next, record your Certificate Password entry in a secure location for later reference. The recorded certificate password is required to install standalone orchestrators or add cluster nodes.