To obtain a Crown of Insight, you have to complete specific events. These events are often limited-timed, so you cannot acquire them once the event is over.

Currently, the only way to get a Crown of Insight is to enter the Dragonspine region and upgrade the Frostbearing Tree to Level 11. However, this will only get you one Crown of Insight.

Here's how to level up the Frostbearing Tree.

In update 1.6, there is a second way to acquire a Crown of Insight, you must take part in the Midsummer Island Adventure and purchase one from the Event Shop, costing 500 Shiny Flotsam.

Three Crown of insights is needed to upgrade a single character fully. Once a talent has reached Level 9, you need a Crown of Insight to reach the max level, Level 10.

This is the only material in the game that every character, new and old, can use.

Once a medium for the storage and transfer of wisdom in ancient times. Now wisdom is found in ancient texts and in profound speech. Nevertheless, this Crown of Insight must still be able to impart some transcendent power and wisdom to its bearer.