Hi, could you elaborate? Are you alluding to, and asking for more/different information than this popular post?
If so, more contributions are definitely welcome here, but just fyi, there have been a few other posts on marginalia that may provide some more info.
Marginalia in general:
How Would a Medieval or Ancient Scribe Go About Writing A (Secular) New Work?
thread in High and Late Medieval Europe 1000-1450
Specific themes:
Tangentially-related threads:
If vellum was so expensive in the Middle Ages, why do medieval books have such large blank margins? - more about the margins themselves: why were they so large and various uses for them (including illustrations)
Why was medieval illustration (especially in calligraphy) so shitty by standards of other periods? Was it only because it was made by (essentially) clerks who did it as an afterthought of calligraphy, or was there more to it? - not so much about the content but more the artistic quality of marginalia