Example:

const position = Cesium.Cartesian3.fromDegrees(
  -75.1699,  // longitude
  39.9522,   // latitude
  100.0      // height in meters
);

const heading = Cesium.Math.toRadians(45.0); // rotation about up axis
const pitch = Cesium.Math.toRadians(-30.0);   // pitch (negative looks down)
const roll = Cesium.Math.toRadians(10.0);    // roll about forward axis

const hpr = new Cesium.HeadingPitchRoll(
  heading,
  pitch,
  roll
);

const modelMatrix = Cesium.Transforms.headingPitchRollToFixedFrame(
  position,
  hpr,
  Cesium.Ellipsoid.WGS84,
  Cesium.Transforms.eastNorthUpToFixedFrame
);

scene.primitives.add(new Cesium.EquirectangularPanorama({
  transform: modelMatrix,
  image: 'path/to/image',
}));

Demo:

• Cesium Sandcastle Panorama