In the MIDI Editor, turn on the velocity at the top by clicking on the button circled in the image below. You'll see the controller box at the box part of the screen. I also turned on the Show Event List button (first button, top left) and you can see the column with the Velocity value.
yes I know that I can adjust the volume AFTER I inserted the note with the mouse, but I want to auto adjust ist BEFORE inserting notes, so that every note I write with the mouse automatically has the right volume. Adjusting the volume after inserting doesnt make sense if you want to compose something, it just takes too much time
. . . . yes I know that I can adjust the volume AFTER I inserted the note with the mouse . . . .
There appears to be some confusion over the terms Velocity and Volume.
What you are wanting to do, ie preset the velocity, is not possible it can only be changed after writing the notes in the MIDI Editor.
Presetting the Volume is possible, however you will find the results unsatisfactory as it is not the true volume but in effect the maximum volume a note can achieve with Velocity determining the loudness of how a note is played.
The key word here is 'played' - writing notes in the MIDI Editor is not the same as playing the notes on a connected MIDI keyboard where the Velocity value as well as the note is read.
Adjusting the volume after inserting doesnt make sense if you want to compose something, it just takes too much time
Just to add a little piece of practical advice: You don't need to manipulate the velocity value for each MIDI note by itself using the standard select (arrow) tool in the MIDI control event editor. You should find raising the values becomes a pretty quick and easy procedure, if you use the draw (pencil) or draw line tools to level the velocity value for all notes at the very top of the chart. Alternatively, you could also do a "select all" (CTRL+A) in the MIDI Editor, and then grab one of the velocity control handles with the regular select/arrow tool. Raising it will raise all velocity events by the same value. So, one way or another, you should be able to maximise all velocity values pretty quickly.