How do I check the status of my G-DRIVE backup?

By "backup" are you referring to Time Machine backups to this G-Drive?

If so, and since this drive is NOT a network drive, the only method to verify the integrity of the drive (& the backups) would be by using the Disk Utillity's First Aid feature.

However, using this feature, will be different whether that drive is formatted in APFS or HFS+. For the latter, you just use that feature with your Mac booted up normally. For the former, you will have to run the Disk Utility in Recovery Mode.

As far as checking individual backups, you can either use the Time Machine interface itself or use third-party apps, like: BackupLoupe or Time Machine Mechanic.