Check out Scott Simmons's in-depth PDF of Apple Final Cut Pro X keyboard shortcuts.
As he writes, "Another reason I made up this menu details is that there are a lot of operations that require a lot different modifier keys to perform. The s key alone can have two and three key modifiers added to it to deal with lots of different audio operations. It’s great we have so many keyboard shortcuts (and great that so many of them are mappable in the keyboard editor) but remembering them all when you aren’t in FCPX on a daily basis can be challenging."
Read more, and download the sheet, here on Pro Video Coalition.