Not sure that "command preview" are you referring to.
Maybe you mean "Transfer options" dialog:
https://winscp.net/eng/docs/ui_copy
If you had started a transfer using drag&drop, that dialog is indeed shown only for the first time, unless you uncheck "Do not show this dialog box again".
You can revert that in preferences:
https://winscp.net/eng/docs/ui_pref_environment#confirmations
Check "Confirmations > Transferring of files" and "Confirmations > Drag&drop operations".

Hi,
As I started a transfer of a very large file there was a message about showing me the command that was about to be executed but in my hast I clicked passed it. I tried another transfer but this time I did not get the message. Would somebody mind sharing the procedure on how to see the command preview. I did try searching but there are so many results that it is difficult to find anything.
Thanks,
Dirk