According to the PMBOK Guide, one of the tools and techniques for developing the project management plan is expert judgement1. This involves obtaining guidance and advice from knowledgeable and experienced individuals or groups, such as subject matter experts, consultants, industry associations, or professional and technical organizations. By consulting a senior project manager within the organization, the project manager can leverage their expert judgement to understand the interdependencies of the work items, the industry standards and best practices, and the organizational processes and policies that may affect the project planning. The other options are not appropriate, as they do not address the issue of the project manager's lack of familiarity with the industry and the work items. Consulting the project sponsor, the product owner, or the senior developer may provide some useful information, but they are not the best sources of expert judgement for the project manager in this situation. References:
* 1: PMBOK Guide, 6th edition, page 89