A typical agenda is to first ask the team what worked well for them and what they did on the project they would like to repeat on another. Then ask what might have been done better or they would do differently the next time. The agenda doesn't need to be any larger than this.
Its usually best to get all the stakeholders involved, including the project sponsor. What I've found is that once the project officially ends, there isn't much interest in meeting on things like this. So a good idea would be to schedule a bit before the project conclusion and perhaps even have an intermediate meeting half way through.