Can OR help with identifying guests who haven't left a review? How can I make this task easier?
If you go to the Bookings tab and switch to list view, hit the Filter button and it will let you filter down to show bookings with or without reviews.
This will only show the ones recorded in OwnerRez, so if you're checking up on bookings from listing sites, make sure to run the channel bridge review imports for those before you run the query so everything's up to date.
In addition to what Chris said, keep in mind that many reviews may be stored (whether manually entered or imported in bulk) globally and not against a specific booking. Airbnb reviews are the only ones that automatically find and match up against bookings at the moment. Other reviews, imported in bulk, will not be linked to a booking.