It the clip section is too big to lasso, split the clip in the midi track.

In case you want to select all track notes, Ctrl+A to select everything and then Ctrl+Right Click on the notes you want to deselect.
If you want to select a large number of notes but not the entire track, decrease the horizontal and vertical zoom for a wider view, then select the desired range and proceed as in the previous case.
Well, this, as in many other cases, is just a workaround.
And now that Sonar is stopped, there are no other solutions in sight.
Let us help each other.

This is easy.
 
In the prv, if you already have some notes selected but want to invert the selection, just click & drag/sweep the virtual keyboard at the left of the the prv and hit the control key before you release the mouse during the drag/sweep

Bristol_Jonesey
This is easy.
 
In the prv, if you already have some notes selected but want to invert the selection, just click & drag/sweep the virtual keyboard at the left of the the prv and hit the control key before you release the mouse during the drag/sweep

 
Excellent, exactly what I was looking for, THANKS. Perfect solution for long large dense midi clips. For microscopic reverse cases I will be using Rogeriodec tip, and just like he said lets stay here together.