public CIMVisualVariable[] VisualVariables {get; set;}

{
    // get the CIM renderer from the layer
    // Note: needs to be called on the MCT
    var cimRenderer = featureLayer.GetRenderer() as ArcGIS.Core.CIM.CIMSimpleRenderer;
    // get the collection of connected attributes for rotation
    var cimRotationVariable = cimRenderer.VisualVariables.OfType<ArcGIS.Core.CIM.CIMRotationVisualVariable>().FirstOrDefault();
    // the z direction is describing the heading rotation
    var rotationInfoZ = cimRotationVariable.VisualVariableInfoZ;
    var rotationExpression = rotationInfoZ.Expression; // this expression stores the field name  
}