Explanation
Obtaining user consent is the best way to mitigate the privacy risk associated with setting cookies on a website. This means that the website should inform the users about the purpose, type, and duration of the cookies, and ask for their permission before storing or accessing any cookies on their browsers. This way, the users can exercise their right to control their personal data and opt-in or opt-out of cookies as they wish.
According to the General Data Protection Regulation (GDPR), consent must be freely given, specific, informed, and unambiguous. The website should provide clear and easy-to-understand information about the cookies and their implications for the users' privacy, and offer a simple and effective way for the users to indicate their consent or refusal. The website should also respect the users' choice and allow them to withdraw their consent at any time.
Implementing impersonation, ensuring nonrepudiation, and applying data masking are not relevant or effective methods to mitigate the privacy risk associated with setting cookies on a website. Impersonation means accessing or using data on behalf of another user, which could violate their privacy and security.
Nonrepudiation means providing proof of the origin, authenticity, and integrity of data, which does not address the issue of user consent or preference. Data masking means hiding or replacing sensitive data with fake or modified data, which does not prevent the storage or access of cookies on the user's browser.

Explanation
The best time during the secure development life cycle to perform privacy threat modeling is early in the design phase, because this will help identify and mitigate the potential privacy risks and vulnerabilities of the system or application before they become costly or difficult to fix. Privacy threat modeling is a systematic process of analyzing the data flows, assets, actors, and scenarios of a system or application to identify and prioritize the privacy threats and countermeasures12. Performing privacy threat modeling early in the design phase will also help ensure that privacy is built into the system or application from the start, rather than as an afterthought.
References:
* CDPSE Exam Content Outline, Domain 2 - Privacy Architecture (Privacy Architecture Implementation), Task 2: Implement privacy solutions3.
* CDPSE Review Manual, Chapter 2 - Privacy Architecture, Section 2.3 - Privacy Architecture Implementation4.

Explanation
The data subject should contact the organization's chief privacy officer (CPO) first if they believe their personal information has been collected and used without consent. The CPO is the senior executive who is responsible for establishing and maintaining the organization's privacy vision, strategy, and program. The CPO oversees the development and implementation of privacy policies, procedures, standards, and controls, and ensures that they align with the organization's business objectives and legal obligations. The CPO also leads the privacy governance structure, such as the privacy steering committee, and coordinates with other stakeholders, such as the data protection authorities, the privacy rights advocates, and the outside privacy counsel, to ensure that privacy is integrated into all aspects of the organization's operations. The CPO is the primary point of contact for data subjects who have any questions, complaints, or requests regarding their personal information, and who can address their concerns and resolve their issues in a timely and effective manner. References: : CDPSE Review Manual (Digital Version), page 21