<apex:page standardController="Account" showHeader="true" sidebar="false" id="page">
  <apex:form>
    <apex:pageBlock mode="edit" id="block">
      <apex:pageBlockSection title="ApexTable" columns="1">
        <apex:inputField value="{!Account.MultiPicklistField__c}" onchange="return changePick();" id="pickFields"/>
        <script>
          function changePick() {
            var options = document.getElementById('{!$Component.pickFields}').options;
            for(var i = 0; i < options.length; i++){
              console.log(options[i].value + ' : ' + options[i].selected);
            };
            return false;
          }
        </script>
      </apex:pageBlockSection>
    </apex:pageBlock>
  </apex:form>
</apex:page>