The character in this sample started out with the first-person standard character, and was modified to add netcode compatibility. You can find a summary of the necessary changes in the Networking the Standard Characters article of the tutorial.
The Character and Player ghost prefabs are located under: Assets/Prefabs/Ghost.
The GhostVariants class defines ghost variants for KinematicCharacterBody, CharacterInterpolation, and LocalTransform for character ghosts.
In this sample game, we use a special strategy for synchronizing character & camera rotation. Due to the fact that we have a character that only ever rotates around its Y axis, it would be a waste of bandwidth to synchronize the full rotation quaternion of the character. Instead, we can simply synchronize the Y euler angle of our rotation, and reconstruct our character rotation on clients/server based on that angle. Similarly, for camera rotation, we only synchronize a pitch angle instead of the full rotation quaternion. These ghost fields are defined in FirstPersonCharacterComponent.CharacterYDegrees and FirstPersonCharacterComponent.ViewPitchDegrees.
In our FirstPersonCharacterAspect.VariableUpdate, when we update our character rotation, we do so by working directly with ViewPitchDegrees and CharacterYDegrees (look for their usage in the parameters of the FirstPersonCharacterUtilities.ComputeFinalRotationsFromRotationDelta call). This function handles modifying those angles, and then computing final character & view rotations from them.
However, since this rotation update is only handled for simulated characters on owning client & server, we also need a way for non-owning clients to synchronize character rotations as well. This is done in BuildCharacterRotationSystem. This system handles rebuilding the rotation of all characters based on the CharacterYDegrees at the beginning the prediction update. With this, all character rotations will be synchronized on all clients, and all character rotations will also be accurately reconstructed on all rollback & resimulation updates