How to activate "OnTriggerEnter" when Player ray hits an object collider?

You shouldn't call the OnTriggerEnter method yourself, as this is a special method for when a trigger event happens.

If you want to execute the code on the player script, which you have in OnTriggerEnter, you should move that code to a seperate method, and call this method from the ray cast.

If you want to execute code on the object your raycast hit (not the player), then it needs a defined script you can search for, with a defined public method, which does whatever it should do when the object is hit.

Example:

 /// <summary>
 /// The players class
 /// </summary>
 public class Player : MonoBehaviour
 {
     void Update()    // Or FixedUpdate() for physical stuf
     {
         RaycastHit hit;
         if (Physics.Raycast(transform.position, transform.forward, out hit))
         {
             if (hit.collider != null)
             {
                 // Find the hit reciver (if existant) and call the method
                 var hitReciver = hit.collider.gameObject.GetComponent<HitReciver>();
                 if (hitReciver != null)
                 {
                     hitReciver.OnRayHit();
                 }
             }
         }
     }
 }
 
 /// <summary>
 /// The component that needs to be added to the other objects which need a callback on a ray hit.
 /// </summary>
 public class HitReciver : MonoBehaviour
 {
     // Called when the player ray hits this object
     public void OnRayHit
     {
         // Whatever you want to happen on a ray hit...
     }
 }

Greetings
Chillersanim