There are companies that aquire designers that have good knowledge in motion design. If I wish to be one of those candidates what exactly must I learn?
Like I said, After Effects is the industry standard. It doesn't matter if there are easier to learn, cheaper alternatives... that's not what most companies use. They use the most professional, most compatible and most productive software that works for them. And more often than not, it's After Effects — which is actually much, much easier to learn than alternative pro apps.
There are companies that aquire designers that have good knowledge in motion design. If I wish to be one of those candidates what exactly must I learn?
Apple Motion (from the app store) works in a similar way to After Effects, i.e. Layered comps.
You may want to start with this as it's much cheaper than a CC subscription.
Then when you learn the basics move on.
I'm not sure if Adobe do a trial of AE...?