Force fsck on a specific unmounted partition:
This is the most common method for checking non-root filesystems.

sudo umount /dev/sdXN  # Replace /dev/sdXN with your partition
sudo fsck -f -y /dev/sdXN

sudo umount /dev/sdXN: Unmounts the target partition. 
fsck cannot be run on a mounted filesystem, especially for 
repair operations.
sudo fsck -f -y /dev/sdXN: