What glider types can be retrofitted with a 'nose' tow hook? Whatglider types cannot?

That's easy to find out.
Go to your manufacturer's website. Examples:
http://www.alexander-schleicher.de/tm/tm_main.htm
http://schempp-hirth.com/index.php?id=30&L=1
Look up the Technical Notes for your glider.
Scroll down until you find "fitting a nose hook" or similar title.
Download.
Contact the manufacturer or rep. Buy the parts for the TN.
Contact a repair station. Install.
Or like most of us, don't. I refused the nose hook when registering what is now Steve's Nimbus 3 in Australia. And used level tow.
But it's good to have two releases.
Yesterday my nose hook failed on launch. The second (successful) launch was on the CG hook, of course in level tow. Other than the lack of failure, couldn't tell the difference.
Jim