Below is a guide on where to find the Soul Ambrosia in Valkyrie Elysium.
Chapter 2
In a chest on the upper level of the church past the second Storage Camp.
O’ Mine Beloved Land
Complete the subquest to receive this Soul Ambrosia as a reward.
Chapter 5
This item can be found in a chest at the cathedral, which is just past the sixth Storage Camp.
Long Lost Reconciliation Subquest
Complete this subquest to receive the Soul Ambrosia as a reward!
Midgardian Studies 2 Subquest
This is a reward from completing this subquest.