<tbody id="co-storebody">
                                                <tr style="display:none;">
                                                    <apex:repeat value="{!speCondscValues}" var="speConds" >
                                                     <apex:variable var="index" value="{!index +1}" />
                                                        <tr>

                                                            <td>
                                                                <div>{!index}</div>
                                                            </td>
                                                            <td>
                                                                <div>{!speConds}
                                                                </div>
                                                            </td>

                                                            <td>
                                                                <div><!--<apex:inputText styleClass="slds-input" style="" id="remarksVal"
                                                                                     />-->
                                                                  <input type="text" class="slds-input" id="{!index}"/><br/>

                                                                     <p id="error" style="color:red;"></p>


                                                                       <!--<apex:inputHidden id="hdnRep2" value="{}"/>    -->
                                                                </div>


//js function This will be called on change of checkbox

Function enableRemarks(checkBox,inputId,speCond){

            var remarks = document.getElementById(inputId);//The id is dynamic
         checkObj = checkBox;
        inputValue = inputId;
        if(checkBox.checked){
            if(remarks.value == ''){
                alert('hihi');
              document.getElementById('error').innerHTML = remarks.validationMessage;
            }
           specConds.push(speCond);
             }

              else{

                specConds.splice(specConds.indexOf(speCond),1);
                  }

        }