Recently we were asked to provide the Subscription Id of the Dynamics 365 Customer Engagement Plan our organization had purchased.
To find the same, follow the below steps
Login to Microsoft Office admin center with administrator account
Quick reference – Admin Center URL(s) in Microsoft Dynamics 365 (Power Platform)
Navigate to Billing >> Your products and select / click on the product.
Copy the id from the URL, which will be the subscription id.
Hope it helps..