– “If a person were to learn anything about the Dhamma, what would be at the top of the list?“
This is just from my own personal journey and experiences. At the beginning when I first started learning from this website, I was reading and learning whatever seem interesting to me at that time. I could say I was all over the place, but then I thought to myself that I should build a solid foundation understanding of the Buddha dhamma and should put more focus on certain teachings. What that meant to me at that time was focusing on the Tilakkhana, specifically on anicca, then onto dukkha and anatta. The amount of time and effort that I have put into learning and practicing the Tilakkhana is approximately anicca 50%, dukkha 35%, anatta 15%. I believe by learning / understanding the Tilakkaha, it would also help me with understanding of the other dhamma teachings as well, such as the four noble truths.
What helped me with learning and understanding the Tilakkhana besides reading / learning from the Puredhamma website is watching / learning from Venerable Waharaka Thero subtitled desana’s.
Venerable Waharaka Thero know the Tilakkhana series
Even though I don’t understand what’s being said besides from the English subtitled, but listening to Venerable Waharaka Thero teach / speak increased my faith and confidence in I was learning from the right teachers / source (Venerable Waharaka Thero, Lal and others). I have mentioned this many times before, but I have never come across any dhamma teacher in my life that teaches / can teach like Venerable Waharaka Thero.
Another important dhamma teaching one should at least get the general idea is Paticca Samuppada. Initially one doesn’t need to know or understand everything about P.S. but very beneficial to at least get the general idea / understanding of it.
What’s mentioned and emphasized here on Puredhamma is that one should stay away from akusala kamma and initial kusala or moral / wholesome deeds as much as possible. From what I have seen you mentioned before about yourself, I’m sure you’re already doing this.
What I found to be beneficial on the path as well is to be flexible with one’s learning and contemplation. What this mean to me is that there are times when I want to focus on a specific dhamma teachings or subjects during contemplation or meditation. But at times no matter how hard I try or want to, nothing comes to mind or my mind doesn’t want to focus on certain dhamma teachings at that time. So I just keep trying to find a dhamma teaching that my mind is willing to latch onto at that moment and go from there. As well everyone has their own characteristic / traits of learning, there might be certain dhamma subjects / topics that’s more suitable to each individual learning at the time.
– “what are the top subjects that a Sotapanna (not a Sotapanna Magga Anugami) undertands?“
Without going into further details, a Sotapanna would know yoniso manasikara. See’s / understands this world as anicca, dukkha, anatta and nibbana as nicca, sukha, atta. Besides contemplating on the tilakkhana, I can’t stress enough the importance of focusing the mind on nibbana as well.
I haven’t / didn’t share everything that would completely answer your questions, but I’m sure others can mention additional insights / information that can benefit you.