I am having a hard time sometimes conceptualizing 'по' when I come across it in my reading.
Take for example a sentence from Bulgakov: 'Трудно сказать, что именно подвело Ивана Николаевича – изобразительная ли сила его таланта или полное незнакомство с вопросом, по которому он писал...'
When I read this sentence, I view the 'по' as 'along' or 'according to,' but doesn't seem to feel right in this context (writing along or according to a question).
If I were to construct a sentence like this myself (from English into Russian)-- 'whether it was the descriptive power of his talent or complete unfamiliarity with the question he was writing about...' I would maybe write it as 'незнакомство с вопросом, над котором он писал' или 'о том, что он писал', but not using 'по.'
To reiterate, what should I know about 'по' so I am in a better position to understand what I am reading or hearing and how can I personally better incorporate it in my speech and writing? I know this is a broad and more theoretical question, but comments and insights are very much appreciated.