I have used a few different journals over the years. The information recorded depended on the purpose for the journal. When I was working to improve my exposure technique, I wrote down info which I could refer back to later to help me understand why certain exposures were not as good as others. When I was learning film development, I kept copious notes on development time, temperature etc. When I traveled to exotic locations, I kept track of where the exposure was made.

A photographer can spend a lot of time and energy keeping notes, but to what end? I think the first step is to figure out why you are keeping the journal. Then figure out the information you need to record to accomplish that goal.