Interesting question.
In my experience, it's really two different things: a chaperone as opposed to a student/trainee observer.
In most cases where I had a chaperone in the room, they really weren't observing. I remember one instance in particular where my female primary care provider had a nurse come in for the genital & rectal exam. The nurse spent the entire exam with her back to us, clearly not paying attention. The wild thought ran through my head to yell "Hey doc! What the hell are you doing!!!" Of course, I only chuckled quietly to myself and let it go.
The only time I can recall a chaperone paying attention was one time, maybe 12-15 years ago. First visit with a new doc. Nurse had me undress completely and don a gown. Doc comes in, she's maybe late 20s / early 30s, heavy set, and very professional. Everything in the exam is "by the book" - from HEENT to auscultation and palpation of my abdomen. She then explains that, per policy, she is required to have a chaperone present if she is going to do an intimate exam, and that I can refuse to have one present and she'll skip that part of the exam. I told her I was okay with it, and she said she'd be right back. She was gone a long time (10 minutes?) and eventually returned with a young lady in scrubs who appeared to be maybe 19 or 20. Doc introduced her simply by saying "this is Julie and she will be the required chaperone for this part of your exam." The doc then had me lay back on the table and pushed my gown up to my belly and did the genital exam with my lying down. She pulled my gown back down and asked me to stand up, when I did I noticed that Julie was facing the exam table, standing a little ways behind the doc. Doc then did a standing genital exam - I purposely didn't make eye contact with Julie and she clearly didn't make eye contact with me - but she didn't face away, either. Then it was turn around & place your chest on the table and spread your legs.
After getting dressed, I was to go provide a urine sample and noticed Julie sitting at a desk worthing on a computer. So I have my doubts if she was a trained medical professional or someone filling in as a chaperone. Nothing like that has ever happened since.
The other scenario - when it's a student or trainee, they always seem to be engaged and paying attention - and the doc (or whoever) frequently has them repeat the exam or procedure (ultrasound tech comes to mind)