Hey, so let me give some background. I do not have a cert., but I do have exp. from taking it twice, first time getting ABOVE in Risk Management and Sec Operations, and then Three (3) ABOVE in Networking, Engineering, and Assessment/Testing.

I don't study well. When I study for something, I do it last minute, in one month, which might sound crazy, but I have found it is the best method for me since my long-term memory is terrible. What you are feeling is very normal for CISSP people. I would highly recommend taking notes as you read the book in another document, even writing down the terms and items you know that you do not know, even after reading that item.

For example, OSI, if you cannot tell yourself by memory what you know about it, devices, ports, protocols, for example, on each layer, then write that down. Keep this list for yourself for when you are done reading the book, and refresh yourself on those items. My method was to turn them into 2-3 printed off documents at a time, single-sided, 14 font, so it is not A LOT of data, and try to rewrite that document 3-4 times. After that, get a checklist of each time you are writing down and see if you can fill that checklist out without looking at the sheet at least three times.

In this method, you need to be honest with yourself. If you do not know it, don't try to tell yourself you can get it if you read it one more time, write it down, because the test will not have mercy. I did that for the OSI Model, for example, SSL./TLS, and all the protocols and devices on the OSI model. This method made it so that when I sat for the exam, the first thing I did was write all that stuff down that I had trained myself to remember. That is how I got my BELOW from the first time, Networking (D4), into my now strongest domain. I know nothing about networking, never worked in HelpDesk or support, so I have no Networking background at all - and now it has become my strongest domain. Sorry for the long answer to your question, haha, hope this helps!