Alt. 1
Open the MIDI Part in the Key Editor. Click in the area that displays the Notes and use ctrl+a to select all the notes.
Alt. 2
Open the Part in the List Editor. Set its filters to only display note data. Use shft+click to select a range of notes.
Alt. 3
Use the Logical Editor & create a Preset to only select note data. Assign this to a Key Command.
Alt. maybe
Not at DAW to look myself. But you can also search the available Key Commands to see if there is a Command to do this. If so assign a key to it.