ObserverManager::observersIdsByEntity

static function observersIdsByEntity(int $entityTypeId, int $entityId): array
{
	$entityTypeId = static::normalizeEntityTypeId($entityTypeId);

	if (empty($entityId))
	{
		return [];
	}

	$dbResult = Entity\ObserverTable::getList(
		[
			'filter' => [
				'=ENTITY_TYPE_ID' => $entityTypeId,
				'=ENTITY_ID' => $entityId
			],
			'select' => ['USER_ID']
		]
	);
	$results = [];
	while($fields = $dbResult->fetch())
	{
		$results[] = (int)$fields['USER_ID'];
	}
	return $results;
}