Basically my teacher said there are a number of different approaches to the journal, and it differs on student to student. The most sound way to record your research is to treat it as a Diary, recount your progress in a recount form, write down your thought processes and ideas as well.
Basically what I am doing, is several concept maps (mind you I'm still very much in the planning stage and not quite into the construction of information) which show the ideas I have, then off-shooting from the central focus is any problems or thought I'm having during the process. I've also got into a habit of writing / copying all the information I've researched and found useful into the journal, and also critiquing the usefulness / reliability of the source to my Major Work.
But yeah, treat it as you want. Just make sure you are recording the processes of your research and also include any important references / sources you discover, and also recount your thoughts, whether that be dot points, a written entry, mind maps, what ever you fancy. Just put everything in there.
I wish you luck for your Major Work! Hopefully this helped you out a little bit.