How do I configure SNMP on ZyXEL router

You can use the commands below to configure SNMP on your CPE:

>sys snmp get
>sys snmp set
>sys snmp trusthost
>sys snmp trap

Fox example:

ras> sys snmp
display get set trusthost
trap discard save clear
ras> sys snmp get

Usage: get
ras> sys snmp get 1234
ras> sys snmp set 1234
ras> sys snmp trusthost 192.168.1.33
ras> sys snmp trap
community destination
ras> sys snmp trap community 1234
ras> sys snmp trap destination 192.168.1.33
ras> sys snmp save

In this example, my snmp manager's ip is 192.168.1.33, and the get community and set commnunity at my manager side is also 1234, when this two commnunity(snmp manager and CPE) match, then you can success to get and set variables of you CPE from snmp manager side.
Also the CPE can send trap messages to your snmp manager.