I am trying to give my player points when an enemy dies

You are keeping Score in the Enemy class. But when you kill the enemy you are destroying the game object. This means that previously Score is not found anymore. If it is not found Unity will just use the default value for a float - which is 0.

You Need to keep the score at a different location. I'll post a solution here soon.

So when looking at Enemy-Player interaction, an easy way is to have a class that is available everywhere.

This is usually the Game Manager script. This is accessable everywhere and doesn't get destroyed on scene change.

 // GameManager.cs
 public class GameManager : MonoBehaviour {
     public static GameManager Instance { get; private set; }              
  
     void Awake()     {
         if (Instance == null) {Instance = this; } else if (Instance != this) {Destroy(this); }
         DontDestroyOnLoad(gameObject);
     }
     
     /* <Future Code Goes Here> */
 }

Now lets add some more logic to this Game Manager that will help use keep score.

 public Score = 0;
 

So now we have a score varaible. If you want to increase the score variable then do it like this.

 public void TakeDamage (float amount)
 {
     health -= amount;
     if(health <= 0f)
     {
         // It might be GameManager.Instance.Score += KillReward
         GameManager.Score += KillReward;
         Die();
     }
 }
 

Also I would highly recommend that your Text object is created in your GameManager isntead of Enemy class. That way you can do this:

 GameManager.Score += KillReward;
 GameManager.scoreText = GameManager.Score;
 Die();
 ...
 

Hope this helps!