The Dragon Eye II is a modernized model of the original that Hiccup created after the original one fell into the volcano. It was first hinted at in "A Matter of Perspective" and was first shown in "The Wings of War, Part 2".
Embarrassed over his obsession over the original Dragon Eye, Hiccup tries to keep his work on the new one a secret, even from Astrid. The work is frustrating and confusing, and he almost gives up. But in "A Matter of Perspective" he's given new inspiration and is determined to finish it.
In "Dawn of Destruction", Fishlegs is tempted to look under a tarp in Hiccup's hut at what he had been working on but decides against it. When the Dragon Hunters compromise Dragon's Edge, Hiccup has Toothless destroy their hut before the Hunters see what he had been working on inside. Thankfully, Fishlegs had retrieved the pieces before the hut was burned, and returned them to him so he could finish it, despite not knowing yet what exactly it was.
The Eye is revealed almost finished in "The Wings of War, Part 2" after it's found that both Viggo and the original Dragon Eye survived the volcano.
Hiccup is seen working on it again in "Snuffnut" with Astrid's help, while talking to Tuffnut.
- “As for the Dragon Eyes, they are such amazing tools for dragon knowledge, but in the wrong hands, they are just too dangerous.”
- ―Hiccup before destroying the Dragon Eyes
In "King of Dragons, Part 1", after obtaining the fifth lenses, Toothless lit up the Dragon Eye II, revealing clues that led the Dragon Riders to the Titan Wing Dramillion on Dramillion Island. After the Titan Wing Dramillion was captured by the Dragon Flyers and released shortly thereafter, the Dragon Riders took it to Caldera Cay for treatment. While under the care of the Defenders of the Wing, the Titan Wing Dramillion produced a never-seen-before flame. Hiccup lit up the Dragon Eye with that flame, causing the map to change and revealing the location of the King of Dragons to be underneath Berserker Island.
During the aftermath of defeating the Dragon Flyers and saving the King of Dragons’ egg in "King of Dragons, Part 2", the Riders decide to destroy both the original Dragon Eye and the Dragon Eye II after realizing how dangerous they could be in the wrong hands.