Being able to view two tracks of MIDI data at the same time is a very useful feature. Maybe you need to see that two tracks are indeed in sync. Or maybe you simply need to see the relationship between two sets of data.
Whatever the reason, this is very simple to set up:
First, highlight both events by clicking on the first, and then clicking on the second while holding the “Shift” key.
Once both events are highlighted, go to MIDI > Open Key Editor. This opens a key editor showing both sets of notes.
One set of notes will look as they usually do when editing MIDI and the other set will look flat; their coloring will be different and the associated velocities will be white. If you click on one of the notes in this second set they switch roles as these become the editable set of notes. Now you can quickly compare and change MIDI note relationships in key and timing without switching editors.