i want to add the ability to zoom on mouse wheel when using PointerlockControls but how to do it ?
You should start by adding an event listener to the
wheel event like this:
document.addEventListener( 'wheel', onMouseWheel, false );
Assuming you are using a perspective camera, you can then try to add a comparable logic like in
OrbitControls by dollyIn/dollyOut the camera along the look direction.