Two add-ons show your layer in WoW Forever: Forever Layer Hop and LayerTracker. Both have files for Forever's 1.60.1 client. Nova World Buffs, which many Classic players used for this, has no Forever version yet: its latest release on 4 November lists only the Classic games. We checked on 10 November.
Forever Layer Hop
Forever Layer Hop (version 0.1.8, 9 November) reads the layer from the IDs of NPCs and vehicles near you, then pools what other users of the add-on see, to build a list of known layers.
The game has no way to list or switch layers directly, so hopping still means joining someone's party on the layer you want. The author warns a Blizzard change to how those IDs work, or to add-on messages, could break it.
LayerTracker
LayerTracker (version 1.7.2) is smaller and only shows your own layer. It reads it from your target or mouseover, and from nameplates if you turn that on.
Why it needs an NPC
Forever doesn't let add-ons read the combat log or list layers, so these add-ons work out the layer from the ID of any NPC you target, mouse over or see on a nameplate. In a city or a busy zone that's instant. Somewhere empty, target any creature first.
Does layer hopping still work
Layers are why a friend can vanish when you group, and why a zone can feel empty or packed. Blizzard lowered how many players share crowded zones on 9 November. See layering in Forever on our sister site for what's confirmed.
Install them like any add-on, see how to install add-ons.