The are two types of power related Leaderboards in the game:

Family Leaderboard
  • Displays individual family ranking based on each player's power
  • You can view your family's power on the top left of your screen, next to your banner
Alliance Leaderboard
  • Displays Alliance ranking based on each Alliance's power
  • An Alliance's power is calculated by combining the power of everyone in it
  • You can view your Alliance's power in the Alliance tab, on the bottom right of your screen
Both Leaderboards can be found by clicking your flag/banner and then tapping the "Leaders" button in the bottom of your screen. Then you can switch between those Leaderboards from the navigation bar in the bottom.

Remember, you get power from any kind of upgrade or training to giving birth to new Nobles, however sacrificing Nobles or losing Troops (by deleting an army of injured troops) will result in your power count decreasing.