Where can I go to see which servers have layering
I don’t even know what layering is.
Every week or so, Blizzard publishes the list as a blue post. You can check the main page of wowhead for recent blue posts, and click Classic for recent Classic news.
Or you can simply go (in-game) to the realm selection page. Each “LOCKED” server has 2 layers. The other servers are all unlayered (1 layer).
Not all locked servers have 2 layers, notably Grobbulus and Earthfury do not.
If the server is locked then it’s probably layered.