Product reviews show up primarily in the product widget. Check to see if you have this widget installed on your product pages.
You can also set your product reviews to show on your onsite and full page widget as well. This can be done by changing their settings under the 'customize widgets' page in the dashboard.
To show the product review widget on the on site widget, turn on the product review visibility under 'settings' on the 'customize review' tab. This guide will help you do that. Do same for the full page widget if you want to show your product review on that widget too.