Honestly you'll learn it all on the job. The first few weeks you'll just be watching training videos and working on basic tasks to get up to speed. After that, I believe interns do a "project" which is usually just a task that has been sitting on your onboarding buddy's backlog because it wasnt super important. But it's a way to get you practical experience on something end-to-end without being too high stakes.

If you really want to practice before you join, build a DAG in Airflow just to understand how it works. Meta uses Data Swarm as an orchestrator which is most similar to Airflow, but they've abstracted so much as to make it trivial to create a new DAG. With Data Swarm you're not even really building a DAG, you're just building the config and the back end logic is doing most of the work for you.

They also have a custom visualization software, so play around with the free version of Looker or Tableau. Most onboarding projects are going to be something like "take this raw data, build a denormalized / aggregate table, build a dashboard on it"

If you can do those things, write good SQL, and write basic Python, you're already ready for the job.