Your journal is entirely up to you. It's a personal approach to display an understanding that you can easily recognise and refer to. You never have to hand in a journal in the final DANCE HSC, so it's really no big deal. It's mainly a study purpose... I did major performance, but majority of my class did major composition. The journal was just an extended version of Core Composition and, to me, it was mainly there to develop an even better understanding of your work when applying it to a viva voce. A major consists of talking for 8 mins, so you should really understand you components for composition BACK-TO-FRONT. Elaborating on each component is something your journal in there for. For instance, Stimulus - don't just write "Inspiration through.. BLAH BLAH BLAH" Actually draw mind maps and show how you developed the entire idea. Where it started, what you want to happen, a title maybe?? It's really up to you.
Have a REALLLLLLLY good understanding of your intent and your journal can really clarify this for you. Basically allow yourself to ask yourself questions in your journal. Put forward both the positive and negative sides for your choices. Propose questions such as "Why" did I choose this intent? "What" do I want to display? "Who" did I want to achieve something from my composition? Just basic questions such as those can relate separately to Space, Time, Dynamics, Abstraction, Motif, Manipulations, Variation, Contrast, Accompaniment, Structure, Repetition, Unity etc...
Overall, the main purpose for your journal is a reflection of your progress. So take the opportunity to discuss elements in your journal. Question WHY the entire time.
I hope that helps you out and Goodluck!