I don't have much experience in journaling, so take this with a grain of salt.
I also have issues with journaling, I always feel like I don't know how or what to write. What got me going most recently was viewing it as a check-in. If I had current goals, what did I do to achieve them. If I was having a tough time, did I shower. If I didn't do what I planned on doing, why? Was it external input (like bad traffic so didn't have time) or internal input (I became really anxious about an interaction) that prevented me from doing something I planned on doing. If I didn't wash my face, was it because I stayed in bed all day or because I finally decided that, yes, I will get up, but just didn't have time to wash my face. Starting from what I did/didn't do in a day was much easier for me. All of those things were easier for me to understand how my emotions affected my day, rather than just going to the emotions. I have also gotten better at recognizing warning signs and triggers, and because I check in, reacting to it and doing something about it.
I haven't read much about Self Knowledge as a discipline, but for me, it's all about reflecting on my decisions, thoughts, and actions, when I can remember to do so.