PoE2 players have started using "Scrying Pool" for two pretty different things, which is why searches feel messy. One points at an Act 3 quest bug, while the other sits deep in Atlas farming, where PoE2 Currency decisions start to matter fast.

The Act 3 pool is a quest problem, not an Atlas trick
The campaign version belongs to The Runeseeker in Act 3. You speak with Farrow in the Mystic Refuge, head back to the Scrying Pool point of interest, and, for some players, the thing just won't respond. Not missing. Not hidden behind a boss. Just dead on interaction, which is honestly the worst kind of quest blocker. The main pain is Runic Knowledge staying locked, because that step can't resolve. Weirdly, it doesn't brick your whole character. You can still push into Act 4, Interludes, and mapping.

Check that you are on The Runeseeker step after speaking with Farrow in the Mystic Refuge.
Try the Scrying Pool interaction once, but don't confuse it with the Nameless Seer mechanic.
If it fails, treat random workarounds as unproven unless current patch notes confirm them.

Endgame Scrying is really about moving card pools
The Atlas version is a whole different beast. There isn't some separate pool object sitting in the map waiting to be clicked. You need the Nameless Seer, and current guide info puts that encounter in eligible Tier 16 maps. When he appears, Scrying lets the map you're running donate its divination card pool to another non-unique Atlas map. The donor keeps its own cards. The recipient loses its native pool and farms the donor's cards instead. That's why people move ugly, valuable pools onto cleaner layouts.

Defiled Cathedral is loved for The Apothecary, but players often hate farming its layout repeatedly.
Tower has Headhunter-related cards, yet its spiral path can feel slow after many runs.
Tropical Island, Dunes, Beach, and City Square work well when speed matters more than native cards.

Reality check: If you're boss rushing for the Seer, you're probably wasting the whole point of the hunt.

Finding the Nameless Seer takes density, not superstition
The best approach is boring, but it works: kill lots of natural monsters quickly. The Seer is described as spawning from those kills, not from the boss, not from a chest, and not from some guaranteed map button. So you roll dense Tier 16s, lean into pack size, and clear in a route that doesn't leave you zigzagging for scraps. Eight-mod maps make sense because more mods can mean more monsters. Monster Lineage Scarabs help for the same reason. Shrines are nice too, especially anything that turns your build into a lawnmower.

Leave near the last scattered monsters if searching them down kills your maps-per-hour rhythm.
Remember that Scrying is character-specific, so your alt will not inherit the setup.
Use an Orb of Scouring on the recipient if you need to clear that Scrying state manually.

What to keep in mind before you lock a pair
Scrying is powerful because it separates card value from map comfort, but it still needs upkeep. Prices move, builds change, and a great donor today might feel average next week. If you're planning long sessions, check your recipient, your Atlas passives, and even your stash before buying cheap poe2 currency for more mapping fuel.