Proofread the following sentences. insert punctuation as required.

After the exam the patients demeanor was improved.
Answer:

After the exam, the patient's demeanor was improved.
* added comma after exam and ? added an ' patients.

You're right.

someone posted answer saying the apostrophe should go after the s in patients (patients')

Not sure if the ' goes after the t - or after the s?

I deleted that response because it was wrong. Your sentence clearly states that it's one patient -- and therefore the apostrophe goes before the s >> patient's

After the exam, the patient's demeanor was improved.