This happens to me quite often, and in such cases I write down on a piece of paper or in the browser / OS notes possible solutions to the problem. For example, ask someone to explain to me; or even give up on the whole thing. In short, I analyze the options for the development of events and their consequences, then I actually make a choice in favor of one or another option. The most important thing is not to panic. From experience I can say that the most effective way is to write a mini-synopsis on a4 sheet and repeat it from time to time right up to the deadline. But again, this is an effective way for me only because of the well-functioning visual memory. Focus on your pluses and you will succeed :)
It all depends on what you mean by the concept of learning. In fact, in 2 days it is almost impossible to come to an orientation in a topic or a problem (especially if you do not understand it), but just memorizing it may work, but this is far from the same thing as learning. I believe you have few options at the moment, so open the book and memorize, use mnemonic techniques and hope for the best.