In Phase 3 of Season of Discovery, players can finally purchase the Dual Talent Specialization to quickly switch between two talent trees outside of battle. To purchase it, however, you'll need to find the NPC selling it.
DUAL SPEC FOUND! How to get Dual Spec in NEW LOCATION in Season of Discovery World of Warcraft
There aren’t many requirements to get Dual Talent; you need to be level 40 and be willing to pay 50 gold for the ability. You also need to find the NPC named Grendag Brightbeard, who is located in Ironforge for Alliance toons and Orgimmar for Horde. He was originally located in Taranis, near Steamweedle Port, but as of this writing he doesn’t seem to be there anymore.
Related: Best Runes for Druid in WoW Season of Discovery
After interacting with Grendag Brightbeard and picking up Dual Talent Specialization, you will gain access to a second skill tree. This secondary tree has the same amount of points as the first, allowing you to create different specs that you can quickly switch between without spending gold. This way, if you want to be able to quickly switch between, say, a healing spec for your Paladin to Ret and back again, depending on what you and your guild are planning or needing.
