Which oscilloscope range to use with the onboard clock???

I don't know about the clock socket, bu I have used buttons etc in the past witout problems (after debouncing) when doing this you need to check the tresholds and max ratings, but I have never used the clock socket. As for the scope what is your changerate? if the signal only changes every other clockcycle you should be right according to nyqvist, but you might need a higher sample rate, on the other hand, why not try the scope you have and see what that does?