Hi There are lot of training materials.
However, if you are looking for specific exercises, my recommendation is
first study all the database tables and identify all Masters, Transaction tables for each module
Example : MM - MARA, is material master, MARD is material stocks
FI - BKPF, BSEG tables etc.
In my opinion this is first step so that you can complete the coding once the requirement is given. (syntax will come quickly, but understanding the process and db relations will take time)