Tore mentioned this to me a few weeks ago and I have made a 'Borderline Bonanza' challenge on my backgammon server where you can test your skills in evaluating these TCTC positions. This is surprisingly difficult (at least to me) but it should be very valuable to practice on.
Also for each position you can then experiment with them by moving one or more pieces and then check how the choice changes. You can do this by drag and drop pieces (on desktop. On tablets you have to click on a piece and then click on the target peg you want to move it to) and then click the 'hint' button.
Once you have extracted all the useful information on a position you can move to the next one. I just checked and there are 247 cube positions that fall inside the equity range -0.015 to 0.015 which is a reasonably amount of positions to try to remember. This will increase as new matches gets added.
You can get even more positions (to view, browse, or play through) if you manually search for positions:
but this will also include positions where equity diff is equal between two choices which doesn't work well when the server needs only one correct answer.
With the manual search you can also narrow your search down to for instance only include opening game positions or many of the other options (some combinations doesn't make sense).
The current highscore is 5. Can you beat it? Surprise me! :-)
I only got 4 but I am working on it...