You can manually split tables with the (not yet documented) command
ALTER TABLE foo SPLIT AT (primary_key_value).
The details of the key encoding is not documented, but you shouldn’t need to know it to compute appropriate split keys. Just choose primary key values from the same distribution as your real primary keys (so if they’re UUIDs, choose either random UUIDs or equally-spaced values throughout the uuid space…)
I don’t think we currently have a good way to inspect the split points. You can dump all the split points of the database (but not in a user-friendly format) with
cockroach debug range ls.