SketchUp Help : Quick reference card
These are nice PDF cards that you can print out and paste near your workstation.
(Download links at the bottom of help article, but be sure your SketchUp version is chosen in the droplist at the top right of the page.)
Also at any time, you can open the Ruby Console (from the Window menu,) a get a listing of the current shortcuts (aka keyboard accelerators,) that are assigned. Use this Ruby one-liner:
puts Sketchup::get_shortcuts
If you want a hash to lookup:
kb = Hash[Sketchup::get_shortcuts.map{|s| s.split("\t")}]
then you can pretty print it:
require("pp")
pp kb
