The title you receive after obtaining all three continental titles is actually a prefix title, unlike the suffix titles received for all the previous steps. The title is simply "Exemplar" and will replace previous titles such as Ambassador, Diplomat, etc.
To gain the title Exemplar you must return to the altar on the Ridge of Memories in Thestra. Once all the titles have been gained from all three continents, clicking on this altar again will give you the title.
At the base of the altar lies a skeleton. Clicking on these bones (You must have the Exemplar title as your current title to click the bones.) will give you another reward: Sign of the Exemplar of All Telon.
NOTE: You may receive the title of Exemplar at any skill level, but you must be diplomacy level 35 or higher in order to receive the reward from clicking on the skeleton. Ensure you are very close to the bones or you will not get the reward; you won't get a second chance to click them.