Which among product backlog, sprint planning and burndown is not an SCRUM framework artifact?

The product backlog is an artifact: it is a list of what is needed for the project, and of the changes that might be needed in the product's development or future. The sprint backlog is an artifact: it refers to any work needed, according to the development team, for the sprint goal to be realised. Artifacts maximize clarity of key information to ensure all on the team share the same understanding of the artifact.

Burndown is not an artifact. At the end of each sprint a burndown chart may be shown by the manager, the horizontal axis showing the sprints; the vertical axis the amount of work remaining at the start of each sprint.