If you go to your home page on Chess.com (My Home), you'll see in the 'New Comments' section, replies to the Tactics Problems you commented on. Any time someone comments on these Problems, you'll see an update in this section 
need help with Tactics Trainer
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Awesome, thank you very much!
Hi, I'm having problem with tactics trainer. I commented a few tactics puzzles and would like to check on answers to my comments. Obviously, I don't remember IDs of these puzzles. Now I can't find the way to identify puzzles I commented. Without ability to do this, the idea of comments is completely useless. Please help me.