How find out if I'm an NSButton with buttonType NSSwitchButton?

A button does not know anything about its style.

From the documentation on NSButton

Note that there is no -buttonType method. The set method sets various button properties that together establish the behavior of the type. -

You could use tag: and setTag: (inherited by NSButton from NSControl) in order to mark the button either as a checkbox or a radio button. If you do that programatically then you should define the constant you use. You can also set the tag in Interface Builder, but only as an integer value (magic number).