In case you still need to know how to do this.
Edit the Registry Key in HKEY_CURRENT_USER:
Software\Microsoft\Microsoft SQL Server\xx\Tools\Shell\Text Editor\Visible Whitespace
Where xx is the version you have (90 is 2005, 100 is 2008)
And set it to 1 to show. Or for SQL Server 2012 and up client tools it is also in HKCU:
Software\Microsoft\Microsoft\SQL Server Management Studio\v\Text Editor\Visible Whitespace
where v in SQL Server 2012 is 11.0 and in SQL Server 2014 is 12.0.