My guess is that you want to click a row in the portal and create a new comments record with the ID of the clicked portal row.
Set Variable [$ID ; value: T10_AddEmployeeToComment::ID_Employee ]
Set FIeld [T40_Comment::ID_Employee ; $ID ]
If you don't want to create a new comment record, just attach the current comment record to the Employee whose portal row was clicked, you only need:
Set FIeld [T40_Comment::ID_Employee ; T10_AddEmployeeToComment::ID_Employee ]
Note that you can select all the fields in the portal row while in Layout Mode and then use Button Setup to turn the selected fields into a button to perform this script. Or you can place a transparent rectangle on top of the fields and set it up as your button (which can produce different "hover" appearance changes not possible with just the fields grouped into a button.)
That worked like a charm...thank you so much. You've saved me hours of experimentation.