Explanation
The best practice for preventing a session from being derailed by an off-topic stakeholder is to use a "parking lot" technique. A parking lot is a list of topics or issues that are not relevant to the current session but may need further discussion or resolution later. The BA should add the stakeholder's concerns to a parking lot for further discussion, and acknowledge that they are important but out of scope for the current session. This way, the BA can keep the session focused on the onboarding process and avoid wasting time or losing engagement from other stakeholders.
References:https://trailhead.salesforce.com/en/content/learn/modules/business-analysis-process-mapping/plan-an

Explanation
This answer chooses user stories as the element that the BA should use to define the intended results of the work based on stakeholder needs. User stories are short and simple descriptions of a feature or a functionality from the perspective of an end user or a stakeholder. User stories can help the BA define what stakeholders want to accomplish, why they want to accomplish it, and how they will measure success. User stories can also help the development and implementation teams to plan product decisions based on stakeholder value.
References:https://trailhead.salesforce.com/en/content/learn/modules/salesforce-business-analyst-quick-look/use

This answer states that identifying personas, documenting the current state, and proposing the future state are the key steps that the BA should take next after identifying the stakeholders, reviewing the project scope, and scheduling each workshop for preparing for the initial requirements gathering workshops with CK on a new Sales Cloud project. Personas are fictional characters that represent the typical users or customers of a product or a service. Current state is how a business process or a system works or operates at present. Future state is how a business process or a system should work or operate in the future. Identifying personas, documenting the current state, and proposing the future state are the key steps that the BA should take next after identifying the stakeholders, reviewing the project scope, and scheduling each workshop because they help the BA to understand and empathize with the users or customers of Sales Cloud, to analyze and document the existing problems or issues with Sales Cloud, and to suggest and validate possible solutions or improvements for Sales Cloud. References:
https://trailhead.salesforce.com/en/content/learn/modules/salesforce-business-analyst-quick-look/use-process-ma