I think you're mainly referring to using the FCK editor. This is only slotted into DNN and not otherwise modified. There's a support forum for it here: http://www.fckeditor.net/forums/viewforum.php?f=6
I know it does have some shortcuts listed in the config file, but they appear to be the standard ones that you would already know:
FCKConfig.Keystrokes = [
[ CTRL + 65 /*A*/, true ],
[ CTRL + 67 /*C*/, true ],
[ CTRL + 70 /*F*/, true ],
[ CTRL + 83 /*S*/, true ],
[ CTRL + 88 /*X*/, true ],
[ CTRL + 86 /*V*/, 'Paste' ],
[ SHIFT + 45 /*INS*/, 'Paste' ],
[ CTRL + 90 /*Z*/, 'Undo' ],
[ CTRL + 89 /*Y*/, 'Redo' ],
[ CTRL + SHIFT + 90 /*Z*/, 'Redo' ],
[ CTRL + 76 /*L*/, 'Link' ],
[ CTRL + 66 /*B*/, 'Bold' ],
[ CTRL + 73 /*I*/, 'Italic' ],
[ CTRL + 85 /*U*/, 'Underline' ],
[ CTRL + SHIFT + 83 /*S*/, 'Save' ],
[ CTRL + ALT + 13 /*ENTER*/, 'FitWindow' ],
[ CTRL + 9 /*TAB*/, 'Source' ]
Perhaps have a look through that forum and see if there's any discussion about it.. let us know if you find anything.
Rob