It would be a "nice to have" the Network ID shown on the Network Wide page (or somewhere else relevant), in order to do a quick endpoint test or create a script quickly, instead of having to go through atleast two API calls, and testing just the find the specific Network ID to use. Especially, if you have many networks in an Organization.
sorry for this - maybe stupid - comment (i have not used the API yet): is the network id not shown in the URL, when accessing the dashboard? or is that cryptic 8-char capital and lower letter string sthg else?
Unfortunately no, the Org/Network ID is not shown in the URL of the dashboard.
To yet the org ID of the organization you have to use the API, to get all orgnanizations you have access to, and then filter the one you need. Then you use the org ID, to get all the network ID in that organization, of which you'll have to filter again to the that one specific network ID you wish to work on.
That's already two API calls just to get the started on the actual task at hand.
Bear in mind, that can be put in the script, but I like to do some one-liners first to make sure I get what I expect. Or just get that single piece of information that I need, via the API.