Get details for a specified custom action:

• command spo customaction get --id <id> --scope|-s [scope] --url|-u <url>
• id of the custom action to retrieve
• scope of the custom action. Allowed values Site|Web|All. Default All
• requires connection to a SharePoint site
• url of the site (collection) to retrieve the custom action from

More information available at https://msdn.microsoft.com/en-us/pnp_powershell/getpnpcustomaction