At the end of each sprint, I make it a point to capture the feedback of the stakeholders on the product increment and the demo presentation. This is a great insight for the development team in the succeeding sprints. It can be used as a KPI for the team to monitor regularly.
To do this efficiently, I make use of available online forms services such as Google Forms and Microsoft Forms. Make the survey easy to fill-up. The survey should be answerable in 2 to 3 minutes with up to 5 questions.
See the sample questions below:

To track the progress overtime, I use a spider or radar chart:

As usual, I provide free templates! Download the template for the Sprint Review Demo Survey Graph below.
Please do share some questions you may ask your stakeholders during a sprint review in the comments below.
– Agile Pinoy