In TaxSlayer ProWeb, scanned documents the taxpayer has sent you can be seen in two places: under the Tools menu for them in the Client List and within the return in the menu under the taxpayer's name at the top of the window. See here for more info.
One reason why you cannot see documents the taxpayer has sent you is that your web browser has a pop-up blocker interfering. If the taxpayer has sent you documents but you're not seeing them, check to see if your web browser's pop up blocker is blocking the Scanned Documents window from showing.
Also, while the documents they have sent you may be visible via the Tools menu, they won't be visible in the return under their name at the top of the window until you get past the Personal Information menu in the return.