in view

               <select class="form-control bookingformfeild diocese_id" name="diocese_id" >
                    <option value="">Select Diocese</option>
                
                    <option data-identifier="Cochin" value="1">Aluva</option>
                    <option data-identifier="Idukki" value="1">Vandiperiyar</option>
                  
              </select>

              

in jquery

              $('body').on("change", ".diocese_id" , function() {
                  var identifier=$(".diocese_id option:selected").attr("data-identifier");
              });

              OR

              $("option:selected", this).attr("data-identifier");