Ok I saw this question in Rita 6th edition at the end of chapter 1.

Lessons learned are BEST completed by?

A. The project manager
B. The team
C. The sponsor
D. The stakeholders

I choose A but the correct answer is D. Here is what the explanation said.

------------------------------------------------------------------------------------------------------------------------------

The best answer is stakeholders as their input is critical for collecting all the lessons learned on each project. The term "stakeholders" include all other groups.