When extracting the contents of a tar.z file, you may be asked what file extension should be used. This usually occurs when WinZip is unable to determine the contents, because of the directory information (or lack thereof) in the .z archive. WinZip then asks you to specify a filename extension for the contents, of which you'll need to have some idea.
Unlike very early versions of WinZip, this issue should only occur if your archive is in the format filename.z. In the case where the filename appears to have two extensions, such as filename.tar.z, WinZip will recognize, from the filename, that the file within the .z archive should have the other extension specified. For this example, WinZip would ask if you want to decompress and open the .tar file.
If you have any questions about this information, please submit a Technical Support ticket.