Gnomes in Hero Storylands are just a bit different than those on the main islands. In Hero Storylands, each Gnome has their own Energy meter!
While you cannot choose which Gnome you will send for any specific task, you can choose which Gnome will receive any Refreshment, or Promotion item you've earned.
Hero Storylands contains 2 new types of special items to help your Gnomes earn Energy: Refreshments and Promotions
Refreshments are items that will appear on the map, and like most items, can be merged together to increase in value. Once they reach a high enough level (any of the final 3 merge tiers), they can be given to one of your Gnomes, to refill some of their Energy.
Why can't I give this drink to my Gnome? --- If you have a Refreshment on your map, but don't see any way to give it to your Gnomes, most likely it isn't at a high enough tier. As you can see in the image above, the 3 lowest level Refreshments do not show 'lightning' icons, meaning, they do not provide any Energy to Gnomes.
These are items that can be merged together, and once the final merge level is reached, the item can be given to one of your 2 Gnomes, to permanently upgrade their maximum Energy total!