Here is the clip from the manual for DHCP Options for the Sophos XG.  Got to keep remembering these!

 

Manage DHCP options dhcp[dhcp-options{add|binding|delete|list}] • To add a custom DHCP option dhcp[dhcp-options {add optioncode 1-255 optionname String optiontype {array-of |one-byte|two-byte|fourbyte |ipaddress|string|boolean }] • To delete a custom DHCP option dhcp[dhcp-options{delete optionname optionname}] • To display all configurable DHCP option dhcp[dhcp-options{list}] • To manage additional options for DHCP Server • Add option to DHCP Server dhcp[dhcp-options{binding add(dhcpname DHCP Server name optionname DHCP options value text)}] • Delete option from DHCP Server dhcp[dhcp-options {binding delete {dhcpname dhcp server name)}] • Show options assigned to DHCP Server dhcp[dhcp-options {binding show {dhcpname dhcp server name)}]

here is a sample from what you would type in to see what you already set:

 

console> system dhcp dhcp-options binding show dhcpname “DHCP Server”
Options Configured from GUI
—————————
Domain_Name
Subnetmask 255.255.255.0
Default_Gateway 192.168.1.1
Domain_Name_Servers
Options Configured from CLI
—————————
TFTP_Server_Name(66) “192.168.1.120”
ciscophone(150) “192.168.1.120”