As a presenter, it is always good to receive unsolicited feedback from the audience. The feedback really helps with future script writing and presentations. What resonated? what was not understood? was the tone right? speed?
As an employee, you will hear numerous presentations, take the time to write a couple of dot points on what worked and not worked for you. Its a great way of raising your brand and showing you care about the company and messaging.
Toastmasters is a great way to develop your speech evaluation skills, so if you want to goto the next level then sign up, it will give you loads of skills to really become an expert evaluator.
So what are you waiting for, send some unsolicited feedback on a presentation you attended.