Thank you, 
I have made an internal varible, called DI90, and I have put it on the page within a PhP windoiw with  question('DI90');  , so now I can at least see it in the dataset.
Then I found some old SoSci documentation about recording clicks, and it seems to create some incremental count function, so I adapted it to record clicking on AD15_05a:
<script type="text/javascript">
function counter(varID) {
  return function() {
    var input = document.getElementById(varID);
    var count = parseInt(input.value);
    if (isNaN(count)) {
      count = 0;
    }
    count++;
    input.value = count;
  }
}
 
document.getElementById("AD15_05a").addEventListener("click", counter("DI90_01"));
</script>
However, nothing gets stored in DI90. Can you help?