Now I know 3 city:
By use /data.json, I can get all dataset for that city.
City of Raleigh
https://data-ral.opendata.arcgis.com/data.json
city of los angeles
https://geohub.lacity.org/data.json
Spokane County WA
https://data-ral.opendata.arcgis.com/data.json
I want more city, I want a full list of all city sub-domain
If I have that full list, I can use below URL to get any cities any dataset.
https://{city-subdomain}.opendata.arcgis.com/data.json
Ok, socrata open data have a full list of domain (233 city county state, etc...)
Here is working sample:
https://transparentgov.net/cleargov1/410/socrata-list-230-organization
In theory, ESRI should (if they have NOT yet) create a FULL list of sub-domain just like what socrata open data did.
Why? you see, any city, county are sub-domain of {city-sub-domain}.opendata.arcgis.com
or hub.arcgis.com/{city-sub-domain}::{layer-name-id}
both url-format above are inter-changeable
I have collect over 1000+ arcgis server list here,
https://transparentgov.net/cleargov1/418/arcgis-list-1000-organization
https://transparentgov.net/cleargov1/764/arcgis-1000-organization
Now I have collect 60+ of {city-sub-domain}.opendata.arcgis.com geohub.arcgis.com/xxx
hub.arcgis.com/xxx
ESRI should maintain this full list, but they have not done yet, I end up do myself to create such list.