TOPIC: PMB

Where, or in what process, is the performance measurement baseline set/developed? I understand it is a part of the project management plan, however, is this set by project sponsor?

Performance measurement baseline (PMB) are the 3 baselines combined: Scope, Schedule and Cost. Each of these baselines are performed in their respective processes and then integrated into "Develop Project Management Plan" process. PMB gets updated as the project progresses.