You can check the number of each unit at [Train Troops] of the Barracks.
■ How to Check the Number of Each Unit
- [Main Screen] > [My Dominion] > [Barracks] > [Train Troops] > [Select Unit]
However, this does not include the troops on board.
Click on the horse riding NPC at the Reviewing Stand to check [Troop Status].
■ Info that can be checked at [Troop Status]
- Stationed troop/food spent/wounded troop/prisoners/number of troops at Reviewing Stand/munition stock (Weapons/Cannons)