The following logs pertain to back up operations:
install_path\NetBackup\logs\bphdb (scheduled backups only)
install_path\NetBackup\logs\dbclient
install_path\NetBackup\logs\bpbkar (Snapshot Client)
install_path\NetBackup\logs\bpfis (Snapshot Client)
Log names are formatted as mmddyy.log, where mm is the month, dd is the day, and yy is the year.