In Preview, the JSON node that shows the data sent to the Response Action is the name of the Response Action itself. In this case, it is ResponseCart. The other nodes show either the input data or the output data of the Integration Procedure.

A Set Values Action in a Value field and a Remote Action in an Additional Output value field can execute a function like CONCAT or DATEDIFF by using the syntax {{function(parameters)}}. For example,
{{CONCAT('Hello', 'World')}} or {{DATEDIFF('2021-01-01', '2021-01-31')}}.

The LWC PubSub Message flag in the Set Values action of the parent OmniScript enables the parent OmniScript to send data to the embedded OmniScript using a custom event. If this flag is not set, the data will not be passed to the embedded OmniScript.

According to the Integration Procedure Actions page, a Calculation Action can be used to "call a Calculation Procedure that performs calculations on input data" and a Matrix Action can be used to "call a Calculation Matrix that performs calculations on input data".

The correct answer is D. Data Mapper Turbo Extract, based on best practices in the official OmniStudio documentation.
From the OmniStudio Developer Guide # DataRaptors # Turbo Extract:
* DataRaptor Turbo Extract is a lightweight, high-performance extract designed specifically for retrieving data from a single Salesforce object, where no data transformation or complex joins are required.
* It is recommended over DataRaptor Extract for performance reasons when only one object and minimal transformation is needed.
Why not the others?
* A. DataRaptor Load is used for writing data to Salesforce, not retrieving.
* B. DataRaptor Transform is used when you need to transform data, not simply extract it.
* C. DataRaptor Extract can be used, but Turbo Extract is preferred for the use case of single object, no transformation - per best practices.
:
Salesforce OmniStudio Developer Guide # DataRaptor Turbo Extract Best Practices OmniStudio Certification Study Guide # "When to use Turbo Extract"