A basic structure of a Delegate in C#

InventoryItemDisplay.cs

public class InventoryItemDisplay
{
  public delegate void InventoryItemDisplayDelegate(InventoryItem item);  // the signature of this delegate <void> <param item>
  public static event InventoryItemDisplayDelegate onClick;                      // the event 

  public void Click()
  {
    Debug.Log("Clicked " + item.displayName);
    if (onClick != null)  // Important null check - if no one subscribes to this event, then it crashes.
    {
      onClick.Invoke(item);                                               // inv
    }
    else
    {
      Debug.Log("Nobody was listening to " + item.displayName);
    }
  }
}

Responder.cs

public class InventoryItemResponder : MonoBehviour
{
  void Start ()
  {
    InventoryItemDisplay.onClick += HandleOnClick;
  }
  
  void OnDestroy ()
  {
    Debug.Log("Unsigned-up for onClick");
    InventoryItemDisplay.onClick -= HandleOnClick;
    
  }
  
  void HandleOnClick (InventoryItem item)
  { 
    Debug.Log ("Behold I have heard of a legendary item " + item.displayName);
  }
  
}