Will make a knowledgebase article soon. Thanks.

Go to the settings section of one of your networks. There's a form for search domain and addresses.

Make up some domain like cool.network and put in your WRT's Zerotier Address (and make sure it's dnsmasq listening on zerotier addresses)

In your clients, turn on Allow DNS. Most clients have a UI for this. On the command line it's zerotier-cli set $network-id allowDNS=1

Now, any queries for like japa.cool.network will go to your router.

This isn't implemented on linux clients. There are too many ways to configure linux networking. zerotier-cli listnetworks -j has the information in it, if you want to make your own thing.

https://zerotier.atlassian.net/wiki/spaces/SD/pages/900431890/DNS+Management

Unfortunately there was no "How to DNS" in the docs, they only said you can configure x y z at my.zerotier.com