How to obtain Zap ID in creates Action

All required information for a Rest Hook to make a callback to a Zap is available in the bundle info you sent to your service during the subscribe request when the user sets up the trigger. 

Perhaps I’m misunderstanding your question, but the trigger does not need to have knowledge of any of the actions in the Zap, and would have no way to invoke or reference them anyway.  Zapier handles all passing of required data to subsequent Zap steps.  In a Zapier integration triggers only need to be concerned with performing that trigger’s logic and returning the trigger’s data.  Actions only need worry about performing their action and returning their specified data, and can’t be concerned about where input data came from and where the returned data might be used by the user.  In other words each operation is atomic from the developer’s perspective and Zapier handles everything else.

To share specific, full workflows, defining specific triggers coupled with specific actions with specific data mapped between steps to perform a specific workflow, you’ll want to look at building Zap Templates/Shared Zaps incorporating your integration.