The warding bond spell says
While the target is within 60 feet of you, it gains a +1 bonus to AC and saving throws, and it has resistance to all damage. Also, each time it takes damage, you take the same amount of damage.
Let's say the Cleric casts warding bond on the wizard. The wizard gets hit for 24 damage. Because the Warding Bond gives him resistance to all damage he only takes 12. Now the (Path of the Ancestral Guardian) Barbarian uses his Spirit Shield feature to reduce this damage by 6.
Does the Cleric receive the initial 12 damage or the reduced 6?