There is currently no key command or shortcuts for common Playing Technique symbols. I searched the forum and found this mentioned in a few threads. For instance https://www.steinberg.net/forums/viewtopic.php?f=246&t=129152&hilit=playing+technique+shortcut and https://www.steinberg.net/forums/viewtopic.php?f=246&t=133606&p=724801&hilit=playing+technique+shortcut#p724801.
I think everyone will have her own favorite list of technique symbols. For cello music, upbow and downbow symbols are used every other bar. Please see attached picture. I know I can call it up using Shift+P, then ‘downbow’. Or I can use the mouse to copy it from note to bar - but that defeats the purpose of keyboard-only note input.