I have no affiliation with the software developer but wanted to share this–and I hope my doing so is allowed in the first place!
It’s a free app I’ve had for about two years now, called Cheat Sheet. For me, this silly little thing has been a lifesaver to learn all of DT’s keyboard shortcuts. All the app does, is display every shortcut for whatever app you have presently active, by holding down CMD for a certain period of time. The delay is user-adjustable. As soon as you let go of CMD, it disappears. I’ll attach a screenshot.
Frankly, I’ve been learning DT features this way, too–the lastest of which was a “linked markdown note.” (I’m a newbie 
)
There’s also a free app called Custom Shortcuts, which the Cheat Sheet guy seems to endorse, in which you can easily reassign the shortcuts themselves. I never used it though.
edit: you see that grey “settings” tab open in the lower-right only because I couldn’t figure out how to take a screenshot of the cheat-sheet being display without letting go of the CMD key. Clicking the settings gear icon kept the view open, so I could take a picture of it.