vRealize Orchestrator workflows that are used for extensibility event Subscriptions require a workflow input titled "inputProperties" that is of the type "Properties". Whenever the workflow is executed from vRA, it will populate this input with all the properties provided by the Event Topic selected in your Subscription. This requirement can be found in the vRealize Automation documentation How do I modify virtual machine properties using a vRealize Orchestrator workflow subscription. The properties that are provided can be seen by expanding the "Schema" of the event as shown:
As you can see in the next screenshot which is from a workflow executed by vRA via the extensibility event for "Compute post provision", the "inputProperties" item contains all of the data listed in the Schema. The provisioned VM's name can be found in the array of ResourceNames. With this value, you can then use vSphere plug-in and built-in workflows in vRO to find the Virtual Machine and create a new snapshot.