I have a question about who is responsible, appart from the Project Manager, for determining the stakeholders´roles. I´m not sure if it´s only the Project Sponsor or any other stakeholder who can help in this activity.
It depends what you mean by "roles". Responsible for Stakeholder management is, in my understanding, the Project Manager, but he or she should get input from as many places as possible, as descriped in PMBOK 220.127.116.11, 18.104.22.168 or 22.214.171.124 on Expert Judgement
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