The logging data is stored onto the microSD card inside OpenSprinkler. The mobile app and web UI support reading and displaying logging data. If you want to retrieve the raw logging data you can take a look at the API documentation:
https://opensprinkler.freshdesk.com/solution/categories/5000022938/folders/5000147084/articles/5000522597-api-documentation-firmware-2-1-1-current-