I am assumimg you have a pair of speakers? Just remove both tweeters and swap them. If the twetter works in the other cabinet, then you have a crossover, (or wiring) problem. If it doesn't work, you need a new tweeter.
Just take the tweeter out and touch the speaker wires to it playing something at low volume. It is most likely the tweeter and not in the crossover though. You need a capacitance meter to check the capacitors.
Why go to the trouble to remove both tweeters just to check one? If you can't check the suspected bad one in it's cabinet, why not just remove it and touch the speaker wires to the terminals and play music through it at low volume?