How to read the field code on the form?

Question

PHP

Hello, there was such a problem. There is a form A with a button on which there is a grid and a set of fields from the datasources of this form. By pressing the button, form B opens with the history of the existence of this field (that is, it shows what data was previously entered in the field, and what is now, respectively), highlighted by the cursor on form A. I believe that in order to get the id of the field on form A, you need to track the position of the cursor ...maybe I'm wrong.
Are there any ideas?
Thanks in advance.