Syntax error, ',' expected

public class bombscript : MonoBehaviour
{
public float fieldofImpact;
public float force;

public LayerMask LayerToHit;

public GameObject ExplosionEffect;

// Start is called before the first frame update
void Start()
{

}

// Update is called once per frame
void Update()
{
    OnCollisionEnter2D(Collision2D col);
    {
        explode();
    }
}

void explode()
{
    Collider2D[] objects = Physics2D.OverlapCircleAll(transform.position,fieldofImpact,LayerToHit);

    foreach (Collider2D obj in objects)
    {
        Vector2 direction = obj.transform.position - transform.position;

        obj.GetComponent<Rigidbody2D>().AddForce(direction * force);
    }

    GameObject ExplosionEffectIns = Instantiate(ExplosionEffect,transform.position,Quaternion.identity);
    Destroy(ExplosionEffectIns,10);
}

void OnDrawGizmosSelected()
{
    Gizmos.color = Color.red;
    Gizmos.DrawWireSphere(transform.position,fieldofImpact);
}
void OnCollisionEnter2D(Collision2D col)
{
    Debug.Log("OnCollisionEnter2D");

}

}

You can’t use OnCollisionEnter2D in Update, OnCollisionEnter2D is called automatically. You can try changing your script to something like

public LayerMask LayerToHit;
public GameObject ExplosionEffect;

// Start is called before the first frame update
void Start()
{
}

// Update is called once per frame
void Update()
{
}

void explode()
{
	Collider2D[] objects = Physics2D.OverlapCircleAll(transform.position,fieldofImpact,LayerToHit);
	foreach (Collider2D obj in objects)
	{
		Vector2 direction = obj.transform.position - transform.position;
		obj.GetComponent<Rigidbody2D>().AddForce(direction * force);
	}
		GameObject ExplosionEffectIns = Instantiate(ExplosionEffect,transform.position,Quaternion.identity);
		Destroy(ExplosionEffectIns,10);
}

void OnDrawGizmosSelected()
{
	Gizmos.color = Color.red;
	Gizmos.DrawWireSphere(transform.position,fieldofImpact);
}

void OnCollisionEnter2D(Collision2D col)
{
	Debug.Log("OnCollisionEnter2D");
	explode();
}

OnCollisionEnter2D() is a function that is called by Unity itself upon detecting that the object has collided with something, not a function that is called every time Update() is called. So you don’t need to call it in the Update() function.