First decide which one you want to copy, and who of the core sovereigns you can find it on. For example Relias.
Go to data/english/CoreUnits.xml in the installation directory and search for a unit with Relias in the <DisplayName>. Inside the same unittype you will find this <CutSceneDataPack>ReliasCutscenePack</CutSceneDataPack>.
Copy that bit and go to Documents\My Games\FallenEnchantress\Units\ and open up the XML for your created sovereign. Search for <CutSceneDataPack> (it will say MagnarCutscenePack) and replace that with ReliasCutscenePack.