Onkeyup for each row of td retrieve from database

Try below code if it works for you

<script>
function kira1(id){
      var LUAS_KESELURUHAN = document.getElementById('LUAS_KESELURUHAN'+id).value;
      var LUAS_KEKOSONGAN = document.getElementById('LUAS_KEKOSONGAN'+id).value;
      
      if (LUAS_KESELURUHAN != "" ){
      remisi = LUAS_KESELURUHAN*LUAS_KEKOSONGAN;
      document.getElementById('REMISI'+id).value = remisi;
      }
}
</script>
$id=1;
while($rowChk = $resultChk->fetch(PDO::FETCH_ASSOC)){
      
            echo "<tr>";
            echo "<form id='makRemisi' method='post'>";
            ?>
            <div style="display:none;">
            <?php
            echo "<div id = 'show_idx'>";
            echo "<td>"?><input type="text" name="LUAS_KESELURUHAN" id="LUAS_KESELURUHAN<?=$id?>" onkeyup="kira1(<?=$id?>)" value="<?php print $rowb["LUAS_KESELURUHAN"] ?>"><?php " 
                </td>";
            echo "<td>"?><input type="text" name="LUAS_KEKOSONGAN" id="LUAS_KEKOSONGAN<?=$id?>" onkeyup="kira1(<?=$id?>)" value="<?php print $rowb["LUAS_KEKOSONGAN"] ?>"><?php " 
                </td>";
            echo "<td>"?><input type="text" name="REMISI" id="REMISI<?=$id?>" value="<?php print $rowb["REMISI"] ?>"><?php "</td>";
            echo "<td>"?><input class="easyui-filebox" name="fileName[]" id="fileName" style= "width:150px;"><?php "</td>";
            echo "<td>"?><div class="show_id"><a href="javascript:void(0)" class="easyui-linkbutton" data-options="iconCls:'icon-add'"></a></div><?php "</td>";
            echo "</form>";
                echo "</tr>";
            echo "</div>"; 
<?
			$id++; // inside your while loop
			?>

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There are a few things you need to fix with your table markup - it is invalid
1. <form> and <div> cannot appear in a table outside of a <tr> <td> .... </td></tr>
2. ID's must be unique - when you are repeating rows you cannot use the same ID

Your function links to the ID of the boxes - and because they are not unique your code will not work.

I modified your Table markup to look like this

<tr>
  <td><input type="text" class="remisi-calc" name="LUAS_KESELURUHAN" value="{$rowb["LUAS_KESELURUHAN"]}"></td>
  <td><input type="text" class="remisi-calc" name="LUAS_KEKOSONGAN" value="{$rowb["LUAS_KEKOSONGAN"]}"></td>
  <td><input type="text" name="REMISI" value="{$rowb["REMISI"]}"></td>
  <td><input class="easyui-filebox" name="fileName[]" style= "width:150px;"></td>
  <td><div class="show_id"><a href="javascript:void(0)" class="easyui-linkbutton" data-options="iconCls:'icon-add'"></a></div></td>
</tr>

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Note I have used HEREDOC syntax to make this more readable.
I removed the ID's
I added a class to the first to text boxes so we have something to bind to.
I made the REMISI textbox readonly
Then the JavaScript I changed to use jQuery as it will make this process a lot easier

<script>
$(function() {
  $('input.remisi-calc').change(function() {
    var parent = $(this).closest('tr');
    var total = +parent.find('input[name="LUAS_KESELURUHAN"]').val() * 
            +parent.find('input[name="LUAS_KEKOSONGAN"]').val();
    parent.find($('input[name="REMISI"]')).val(total);
  });
});
</script>

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For this to work all you need to do is add the jQuery library

You can see this working here