How can I add the OnTriggerEnter function to all game objects that I instantiate?

Questions & Answers
1

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class GasolineScript : MonoBehaviour
{
public GameObject Gasoline;
public GameObject Coin;
int n = 0, moveSpeed = 6, ok;
float aux1,aux2;
bool isMoving = false;
Vector2 dir, pos;
GameObject gasoline;
Rigidbody2D gasolineRB;
BoxCollider2D gasolineCol;

void Start()
{
    SpawnCoins();
}

void Update()
{
    if (isMoving)
    {
        gasolineRB.MovePosition(gasolineRB.position + dir * moveSpeed * Time.fixedDeltaTime); 
    }
    
    if (Input.GetMouseButtonDown(0))
    {
        gasoline = Instantiate(Gasoline, new Vector2(-2.7f , 0.1f), Quaternion.Euler(0f, 0f, 180f)) as GameObject;
        pos = Camera.main.ScreenToWorldPoint(Input.mousePosition);
        isMoving = true;
        gasoline.AddComponent<Rigidbody2D>();
        gasolineRB = gasoline.GetComponent<Rigidbody2D>();
        gasolineCol=gasoline.GetComponent<BoxCollider2D>();
        dir = (pos - new Vector2(-2.7f, 0.1f) ).normalized;
    }

    //rotation
    transform.eulerAngles = new Vector3(0, 0, n);
    n++;
}

void SpawnCoins()
{
    aux1 = Random.Range(-3.9f, -1.55f);
    aux2 = Random.Range(-0.9f, 0.9f);
    ok = 1;
    for(;ok==1;)
    {
        ok = 0;
        if((aux1>=-3f && aux1<=-2.4f) && (aux2<=0.4f && aux2 >= -0.2))
        {
            ok = 1;
        }
        if (ok == 1)
        {
            aux1 = Random.Range(-3.9f, -1.55f);
            aux2 = Random.Range(-0.9f, 0.9f);
        }
    }

    GameObject coin= Instantiate(Coin, new Vector2(aux1,aux2), Quaternion.identity) as GameObject;
}

void OnTriggerEnter2D(Collider2D collider)
{
    if (collider.gameObject.tag == "Coin")
    {
        Destroy(collider.gameObject);
        SpawnCoins();
    }

    if (collider.gameObject.tag == "Border")
    {
        Destroy(gameObject);
    }
}

}

2

To further my comment here is an example OnTriggercomponent script and its usage.

Example OnTriggerEnterComponent

public class OnTriggerEnterComponent : MonoBehaviour
{
    public string ActionableTag { get; set; }

    private void OnTriggerEnter2D(Collider collision)
    {
        if (collision.CompareTag(ActionableTag))
        {
            // Do Something
        }
    }
}

Demo of its usage

public class Demo : MonoBehaviour
{
    public GameObject prefab;
	
	private void Start()
	{
        GameObject go = Instantiate(prefab, Vector3.zero, Quaternion.identity);
        go.AddComponent<BoxCollider2D>();
        go.GetComponent<BoxCollider2D>().isTrigger = true;
        go.AddComponent<OnTriggerEnterComponent>().ActionableTag = "Player";
	}
}

Also as you can see i changed it to use CompareTag as it is more efficient., Hope this helps.