Hi,
You should know where your application is saving files, if so getting full path name is easy,
String filename=QestionsFU.PostedFile.FileName;
this actually returns the client filename. Meaning the path to the specified file. Supposed your app save all files under C:\UPLOADED_FILES\ in server.
then full file name will be
String filename="C:\UPLOADED_FILES\"+QestionsFU.PostedFile.FileName;
so you have the full path now.