Hello,
ok I´ve read here, that joystick movement is not possible to record in SEQ .
So it looks like that the aftertouch is also not possible to record.
Is that right?
You are correct. 
Add it to the feature request thread.
This has been requested since the A4 was released and ignored. It’s a performance technique that is essential and at least for me, it’s creativity killjoy having to go in per note/step/event and “add” velocity and after touch on my A4 with a keyboard attached. It’s simply midi after all! I think they would have implemented this already by now if they had any intention of doing so. I had even bought an KMI QuNexus when I firstly got my A4 thinking this was possible but alas, nope!