While traveling the world map you may receive a pop-up message telling you that a new slot for storing a character ability is available. This happens only if you have an available slot in the level 5, 10, 15, 20, 25 or 30 locations, but it doesn't matter which. The quest will select the lowest level that is still open as the slot that is targeted. This means that if you have levels 5 & 10 open then the quest will inform you that your level 5 slot is unassigned. In order to complete the quest you'll need to visit the Player Abilities interface and select an ability for that slot. As there is no expiration or consequence for failure this quest will remain active until that slot is filled.