First off, you cannot run a process via API in Community Edition. You must have Enterprise Edition and a bot runner.

Second, you can get the process ID in the URL when the process is being edited. Example:

https://aa-devx-dev.my.automationanywhere.digital/#/bots/repository/private/files/36125/module/hbc/process/edit

The process ID is 36125 in this case. You can do the same with task bots, which also cannot be executed by API in Community Edition.