There isn't really a way to view what's in a BAK file without actually restoring it to your logbook.
If you want to do that, here's the process I would recommend.
1. Create a backup of your current, most up to date logbook (the one missing 5 entries).
2. Find the previous BAK you want to reference and restore your logbook to that backup.
3. Find the missing entries and write them down somewhere.
4. Restore the most current BAK (with 5 missing entries) and add those missing entries manually.