To get an overview, where you can see error messages:
# All messages
Get-WinEvent "Microsoft-Windows-Backup" | Format-Table -Wrap
# Only the newest
Get-WinEvent "Microsoft-Windows-Backup" -MaxEvents 1 | Format-Table -Wrap
To get EventData with details like information about volumes, you can use this code:
# Save as variable
$Event = Get-WinEvent "Microsoft-Windows-Backup" -MaxEvents 1
# Convert to XML
$EventXML = [xml]$Event.ToXml()
# Show all EventData
$EventXML.Event.EventData.Data | Format-Table -Wrap
# Show only VolumesInfo data, with things like path, size and number of files
$EventXML.SelectSingleNode("//*[@Name='VolumesInfo']")."#text"
That can of course be parsed further, but with these commands you can get the information.
Sample output from my server:
TimeCreated Id LevelDisplayName Message
----------- -- ---------------- -------
21-02-2018 23:12:16 14 Information The backup operation has completed.
<VolumeInfo><VolumeInfoItem Name="D:" OriginalAccessPath="D:"
State="14" HResult="0" DetailedHResult="0" PreviousState="8"
IsCritical="0" IsIncremental="1" BlockLevel="0" HasFiles="1"
HasSystemState="0" IsCompacted="0" IsPruned="0" IsRecreateVhd="0"
FullBackupReason="0" DataTransferred="6274990320"
NumUnreadableBytes="0" TotalSize="5118410992" TotalNoOfFiles="4691"
Flags="84" BackupTypeDetermined="1" SSBTotalNoOfFiles="0"
SSBTotalSizeOnDisk="0" /></VolumeInfo>