I would have made a place for the Dojo (can be multiple) in a place hierarchy,
then add the Teacher/Master as a person (then you can also do this Master’s family lineage if you want to)
then add as many Class Events (events can be as long as you need) to that Teacher as Shared Events, you will then be able to add a custom role for the person, add attributes and notes that a specific for that person etc.
Then do the same for any students that participated in those classes with custom roles and any attributes you like, e.g., Grades etc.
Usually a student would evolve, also in martial arts and move up to new “classes” as they get better/older.
You can add shared events to both family members and non-family members.
If you can’t find a report that have the features you need, you can try a feature request.
An alternative for your type of research is to use an advanced timeline software like Aeon Timeline 3 (not free or open source, not Linux), but it has limited reports… you can visualize what you need in it though.
Another alternative is to use Obsidian and build up your research in notes for places, teachers, students, families and members, events, sources etc., adding wikilinks with descriptions etc. in each of the notes as you like, in free form or structured text forms, then use some of the many add-ons for generating timelines, lineages for dojos/teachers/students etc.
You will have a network graph for all the links and tags so you at any time you can see the relations, and you can filter what you like, add some colors to the nodes (notes) in the graph based on your notes YAML etc. etc.
I use this approach for all my research on the Norwegian Mercantile Fleet, where I have links from ships to journeys to sailors and owners and passengers, as well as having links from journeys to ports, and all is linked to a huge number of sources via citations.
In addition, I can add images to the different notes.
There is a longform addon that can be used if you like to make longer articles or books that holds a selection of your notes, there is map addons, timeline addons etc. etc.
just some tips for how you can solve your research.
EDIT:
I should add that you of course can add all your markdown Notes to your Gramps objects as media files.