What I should do when I have a good guess, but I am not sure if I am right. So, I would like only to comment, but I do not have reputation for that. What is the approach in these cases?
I'll just convert this into an answer:
Wait until you have more reputation. It only takes 50. Shouldn't take long to accrue.
You need 33 more reputation to be able to comment anywhere you please. If you want to contribute enough to make comments, surely you can attain that privilege!