How to share varibles betweent scripts

you use a component lookup like this:

 GetComponent<nameOfScriptYouAreLookingFor> ().somevariable = true;

There are many ways, here is one:

In the weapon's shoot function:

 GameObject proj = Instantiate( //your instantiate code );
 proj.GetComponent<Projectile>().Init(this); //pass reference to this instance

Put this in Projectile:

 public Weapon m_Weapon;
 
 public void Init(Weapon weapon)
 {
      m_Weapon = weapon;
 }

then in your deal damage code

 other.GetComponent<EnemyHealth>().TakeDamage(m_Weapon.damage);

Here needs be considered the architecture and logic. Most likely a Weapon should include a projectile as it is the logical way of things (You use a certain type of bullet with a given rifle in real life, not the other way around).

So your weapon class would include the Projectile it is using. This way you can pass how much damage a projectile should do based on what weapon is using it, just like in real.

Your weapon class should handle the input so when user presses a button, a projectile is created (or used from a pool) and the damage value is given to it.

 public class Weapon : MonoBehaviour
 {
       [SerializedField] protected GameObject projectile;
       [SerializedField]protected float damage;
       protected virtual void Update(){
            if(Input.GetKeyDown(KeyCode.Space)){  CreateProjectile(); }
      }
      protected virtual void CreateProjectile(){
            GameObject obj = (GameObject) Instantiate(this.projectile);
            obj.GetComponent<Projectile>().Init(this.damage);
     }
 } 

 pubic class Projectile : MonoBehaviour
 {
       [SerializedField] protected float initialDamage;
       protected float actualDamage;
       public virtual void Init(float weaponDamage){  
              // Here we could say that projectile has initial damage that is multiplied by weapon damage
              this.actualDamage = this.initialDamage * weaponDamage;
       }
       protected virtual void OnCollisionEnter(Collider other)
        {
           EnemyHealth ea = other.GetComponent<EnemyHealth>();
           if(ea == null){ return; }
           ea.TakeDamage(this.actualDamage);
        }
 }

Notice that most methods and references are protected and/or virtual. This is because you should make your Weapon and Projectile classes as abstract. You don't find a weapon in real, you find a AK-47 that is a weapon. So you could consider a subclass Ak that inherits from Weapon and takes care of its own data.

As for the code, when the space bar is pressed down, it will create a new projectile and on creation, it will pass down some data (there could be more than just a float). This is simple but could get you going in a good direction.

I am assuming your Weapon class can make things like Axes, Swords, and projectile throwing weapons like Arrow/Bow and Throwing Knives. If this is a correct assumption then you can do something like this:

   public class Projectile : MonoBehaviour 
      {
     // Get a reference to the Weapon that created this Projectile. You would set this in the inspector. 
     public Weapon weapon; 
     
     // Since the variables in your Weapon class are public you can call on them like this:
     Debug.Log(weapon.damage); 
     
            void OnCollisionEnter(Collider other)
             {
               if(other.GetComponent<EnemyHealth>() != null)
               {           
                  other.GetComponent<EnemyHealth>().TakeDamage(weapon.damage);
                }
            }
      }