Buscar objetivos

Collider[] objetivos =
    Physics.OverlapSphere(
        transform.position,
        radio,
        layerEnemigos
    );

Aplicar daño

foreach (Collider col in objetivos)
{
    if (col.TryGetComponent<IDamageable>(
        out IDamageable damageable))
    {
        damageable.RecibirDaño(daño);
    }
}

Visualizar

void OnDrawGizmosSelected()
{
    Gizmos.DrawWireSphere(
        transform.position,
        radio
    );
}

Resumen rápido

Physics.OverlapSphere(...)
TryGetComponent<IDamageable>()