Final answer:
CHKDSK is the best tool to diagnose and repair disk errors reported in the Event Viewer, as it checks the file system and metadata and attempts to fix various types of errors.
Step-by-step explanation:
The best tool to diagnose multiple disk errors noted in the Event Viewer is CHKDSK (Check Disk). CHKDSK is a Windows utility that can check the file system and file system metadata of a volume for logical and physical errors. If it finds any issues, it will attempt to repair the problems related to bad sectors, lost clusters, cross-linked files, and directory errors.
Other tools mentioned, like FDISK, BOOTREC, and DISKPART, serve different purposes. FDISK is used for disk partitioning and is not typically used for diagnosing or repairing disk errors. BOOTREC is used to repair boot issues, and DISKPART is a command-line tool for managing disk partitions.
Therefore, if a technician encounters disk errors in Event Viewer, CHKDSK is the appropriate tool to use to diagnose and potentially fix those disk errors.