Displaying alert message when Reopen button or link is clicked for closed request

I have a requirement to display an alert message whenever an user tries to reopen a closed request using the Reopen link at top or the Reopen button at bottom.

I tried giving the alert message in the onclick() event of the Reopen button in the InRequestDetails.htm. But its not at all working. I have Service Manager v9.0.6.94.

I have also browsed through other htmls and JS files, but unable find the place where the reopen functionality is implemented. Any solution or clue on this will be really appreciated.

Thanks,

Praveen S