There is no get function for that.
When you specify the input field, you also select a field in your database table into which the data from that input box in the dialog will be entered if the user clicks a button in the dialog that is specified to commit the data. (In fileMaker 11 and earlier, only button 1 commits data. In FileMaker 12, you can specify a commit option for any/each of the buttons.)
Thanks I see now