Product Owner is part of the Scrum Team, so he/she needs to collaborate with the team members when they have questions related to working in the Sprint.
At the same time, the Product Owner represents the interests of the stakeholders, so he/she needs to engage and collaborate with them as well

Scrum Guide
The purpose of the Sprint Review is to inspect the outcome of the Sprint and determine future adaptations. The Scrum Team presents the results of their work to key stakeholders and progress toward the Product Goal is discussed.

Scrum Guide
Work cannot be considered part of an Increment unless it meets the Definition of Done.
If a Product Backlog item does not meet the Definition of Done, it cannot be released or even presented at the Sprint Review. Instead, it returns to the Product Backlog for future consideration.

Scrum Guide
Product Backlog items that can be Done by the Scrum Team within one Sprint are deemed ready for selection in a Sprint Planning event. They usually acquire this degree of transparency after refining activities. Product Backlog refinement is the act of breaking down and further defining Product Backlog items into smaller more precise items. This is an ongoing activity to add details, such as a description, order, and size. Attributes often vary with the domain of work.

Scrum Guide
Sprint Planning initiates the Sprint by laying out the work to be performed for the Sprint. This resulting plan is created by the collaborative work of the entire Scrum Team.