By default, Ctrl+K, C to comment, and Ctrl+K, U to uncomment. You can always change the keyboard shortcuts.
If you need to toggle Comment/Uncomment, you will need to write a macro like this:
s = document.selection.Text;
if( s.length == 0 ) {
s = document.GetLine( document.selection.GetActivePointY( eePosLogical ) );
}
if( s.length >= 2 && s.substr( 0, 2 ) == "//" ) {
editor.ExecuteCommandByID(4372); // Uncomment
}
else {
editor.ExecuteCommandByID(4371); // Comment
}
This macro assumes the first two characters of a comment line is //
.