/usr/share/nagios-plugins/templates-basic/disk.cfg is in nagios-plugins-basic 1.5-3ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 | # 'check_disk' command definition
define command{
	command_name	check_disk
	command_line	/usr/lib/nagios/plugins/check_disk -w '$ARG1$' -c '$ARG2$' -e -p '$ARG3$'
	}
# 'check_all_disks' command definition
define command{
	command_name	check_all_disks
	command_line	/usr/lib/nagios/plugins/check_disk -w '$ARG1$' -c '$ARG2$' -e
	}
# 'ssh_disk' command definition
define command{
	command_name	ssh_disk
	command_line    /usr/lib/nagios/plugins/check_by_ssh -H '$HOSTADDRESS$' -C "/usr/lib/nagios/plugins/check_disk -w '$ARG1$' -c '$ARG2$' -e -p '$ARG3$'"
	}
####
# use these checks, if you want to test IPv4 connectivity on IPv6 enabled systems
####
# 'ssh_disk_4' command definition
define command{
        command_name    ssh_disk_4
        command_line    /usr/lib/nagios/plugins/check_by_ssh -H '$HOSTADDRESS$' -C "/usr/lib/nagios/plugins/check_disk -w '$ARG1$' -c '$ARG2$' -e -p '$ARG3$'" -4
        }
 |