The super smart and to-the-point @DanRathbun knows a quicker, easier way, without plugin:
which is (for those too lazy to read through the post to find it:
Window - Ruby Console - Paste this: puts Sketchup::get_shortcuts
and copy out the list 
Further, allow me to +1 @mleikos suggestion: “Why couldn’t you show them in the instructor, or better yet, right next to the tool button?”
Because, while learning is all easy for academics I trust, your phone and every other device still has helpful reminders (numbers, even letters) on each key. Guess why? 
It doesn’t harm you or anyone to follow his suggestion, hence +1, but helps millions here.
-1 for the “two key” shortcut though: because that slows down massively IMHO. The alt, shift, ctrl are easier to reach, yes, you are right there.