Melee Attacking script doesn't work

Hey guys, beginner here. I recently attempted to make my players take damage when two objects collided. When one player would press the attack button, the gameobject that I created (to represent the sword of the player) 'touches' player2. However, nothing happens. I'm sure that class playerattack works, but class attacktrigger doesn't. Thank you

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class PlayerAttack : MonoBehaviour {
     private bool attacking = false;
 
     private float attackTimer = 0;
     private float attackCd = 0.3f;
 
     public Collider2D NinjaAttackTrigger;
 
     private Animator anim;
 
     void Awake(){
 
         anim = gameObject.GetComponent<Animator>();
         NinjaAttackTrigger.enabled = false;
     }
     void Update() {
         if (Input.GetKeyDown (",") && !attacking) {
             attacking = true;
             attackTimer = attackCd;
 
             NinjaAttackTrigger.enabled = true;
 
         }
         if (attacking) {
 
             if (attackTimer > 0) {
                 attackTimer -= Time.deltaTime;
 
             }
             else {
                 attacking = false;
                 NinjaAttackTrigger.enabled = false;
             }
         }
         anim.SetBool("Attacking", attacking);
     }
 
 }

ATTACK TRIGGER STARTS HERE

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class AttackTrigger : MonoBehaviour {
 
     public int dmg = 10;
 
     void onTriggerEnter2D (Collider2D col) {
 
         if(col.isTrigger == true && col.CompareTag("Knight")) {
             col.SendMessageUpwards ("Damage", dmg);
             dmg--;
             print("working");
     }
     }
 
             }