In the 17th episode of season 1, Alex asks J'onn Jonzz
When will I be ready?
to which he responds
When you can beat me.
This is also shown in the first episode of the 4th season when Alex is training Jensen. She doesn't appear to actually instruct him, she just says
and when Jensen fails, she doesn't actually show him what to do next time, or what he did wrong, she simply says
Why does the DEO train this way, if it is not possible to learn something without being taught?