Foundations
The computer-science and data-systems core — taught for this job. This is the course that turns you from someone who can use tools into someone who understands why they work, so you can reason about new ones, debug the weird failures, and design rather than copy. It's the degree-equivalent material, pruned to what a data platform engineer actually uses, and grounded in concrete examples throughout.
Foundations is the longest course and the one that pays off the most. Every later course — the craft, the tooling, the capstone — assumes the ideas here. Take it slowly; do the exercises. You can always reference back, and the schedule budgets the most time for exactly this course.
Tools change every few years; foundations don't. An engineer who knows why a columnar format is fast, why a join can blow up memory, and why exactly-once delivery is hard can pick up any new tool in days — and debug the problems that stump people who only memorized commands. That durability is the entire point of this course.