This version of Unity is unsupported.
Method group is Obsolete

InteractionSourceState.headPose

Obsolete Support for built-in VR will be removed in Unity 2020.1. Please update to the new Unity XR Plugin System. More information about the new XR Plugin System can be found at https://docs.unity3d.com/2019.3/Documentation/Manual/XR.html. public Pose headPose;

Description

Head pose of the user at the time of the interaction.