According to the BABOK® Guide, implementation subject matter experts are "stakeholders who have specialized knowledge of the technologies, tools, or techniques that will be used to implement the solution" (p.
15). They need detailed technical interface requirements to understand how the solution components will interact with each other and with external systems. Technical interface requirements specify the characteristics, formats, protocols, and standards of the data exchange between the solution and other systems (p. 36). The other options are not correct because:
Project manager is "the stakeholder who is accountable for the delivery of a specific project" (p. 14).
They need high-level information about the requirements, such as scope, schedule, budget, and risks, but not detailed technical interface requirements.
Testers are "stakeholders who are responsible for verifying that the solution meets the specified requirements and quality standards" (p. 15). They need testable and measurable requirements, such as functional, non-functional, and quality requirements, but not detailed technical interface requirements.
Regulators are "stakeholders who have the authority to impose rules or standards on the solution or the domain" (p. 15). They need compliance and regulatory requirements, such as legal, ethical, and social requirements, but not detailed technical interface requirements. References:
BABOK® Guide, p. 14-15, 36
Everything You Wanted to Know About Interface Requirements, section "What is an Interface Requirement?"