var j = 0;

while (j <= i) { //i is the variable passed from php, containing the number of useres

    j++;

    $('#btnEdit'+j).click(function() {

        $("#prename"+j).removeAttr('disabled');
        $("#surname"+j).removeAttr('disabled');
        $("#function"+j).removeAttr('disabled');
        $("#prefix"+j).removeAttr('disabled');
        $("#phone_number"+j).removeAttr('disabled');
        $("#email"+j).removeAttr('disabled');


    });


}

<label>Prename</label>
<input name="prename" id="prename<?php echo $i; ?>" value="<?php echo $row['db_prename_value']; ?>" maxlength="100" type="text" placeholder="Prename" disabled="disabled" />

<input type="button" id="btnEdit<?php echo $i; ?>"
name="button<?php echo $i; ?>" value="Edit"></input>

$('#btnEdit'+j).click(function() {