All your Nobles start at level one and they max out at level 40. To level them up you either need Noble XP or Family XP. You cannot level up your Nobles to level 40 right away, each Talent tier unlocked also unlocks 10 levels for each one of your Nobles.

Noble XP cannot be tracked as a whole. Each Noble accumulates their own XP as they perform actions. This XP can be spent on increasing your Noble's level and stats through a Noble's profile page. From main page, tap on the "Family" tab then choose a Noble to see their profile.

Family XP can be tracked as a whole, as it's a different XP resource that can be used for any Noble of your choice, if they've not accumulated enough Noble XP to level up.

You can earn Noble XP or Family XP from most activities you perform with your Nobles, including:
  • Exploring a dungeon
  • Commanding an army in battle
  • Trading at a trade post
  • Claiming event rewards
  • Performing Noble actions such as Boink, Bribe, Assault, Capture and Execute

Noble XP is suited only for one Noble and Family XP is a consumable item to promote certain Nobles. Family XP can be acquired from chests and rewards for events. Noble XP can be acquired through specific noble actions like trading, exploring dungeons, commanding armies etc.

Keep in mind, that if the action you're performing is related to your Noble's role, then more Noble XP will be awarded!