What is the best way to import data in WissKI entities, after I created the paths? It seems to me that you already managed this for Herbarium Erlangense.
yes, your guess is right. The data has been imported with the wisski_sql_import module (in Drupal 8 called wisski_odbc_import) from a mySQL database.
The import module covers the typical cases where you need to import tabular data from a relational database or a spreadsheet.
You will need to write an xml file that defines where to find the data and how to map it.
There is a short german description of the file's basic structure here.