The two effective ways for the Scrum Team to make non-functional requirements visible are C and D.

C. Add them to the Definition of Done so the work is taken care of every Sprint.

The Definition of Done (DoD) is a shared understanding of what it means for a Product Backlog item to be complete and potentially releasable1. The DoD can include non-functional requirements that apply to the entire product or system, such as performance, security, usability, etc. By adding them to the DoD, the Scrum Team ensures that they are met every Sprint and that the quality of the product is maintained2.

D. Add them to the Product Backlog to ensure transparency.

The Product Backlog is an ordered list of everything that is known to be needed in the product1. The Product Backlog can include non-functional requirements that are specific to certain features or functionalities, such as response time, availability, scalability, etc. By adding them to the Product Backlog, the Scrum Team ensures that they are visible to all stakeholders and that they are prioritized and refined along with the functional requirements3.

A and B are not effective ways for the Scrum Team to make non-functional requirements visible.

A. Run the integration and regression tests before the end of the Sprint, and capture the open work for the Sprint Backlog of the next Sprint.

This approach does not make non-functional requirements visible, but rather postpones them until the end of the Sprint. This can lead to incomplete or low-quality Increments that do not meet the expectations of the customers or users. Moreover, this approach does not account for any changes or feedback that may occur during the Sprint4.

B. Put them on a separate list on the Scrum board, available for all to see.

This approach does not make non-functional requirements transparent, but rather isolates them from the functional requirements. This can lead to confusion or inconsistency in how they are handled by the Scrum Team. Moreover, this approach does not align with the principle of having a single source of truth for the product requirements, which is the Product Backlog5.