I have a Rowe AMI 100 CD jukebox. It plays about 3 song and then right upper speaker goes out. Is this a speaker problem or something else?

You have not given enough information to make a proper diagnosis. The first thing to check is if the bottom bass speaker is working when the top speaker goes out. If it is then you can easily check the top speaker by jumpering from the working speaker to the one not working. Odds are it is not the speaker. It could be amp connections as the other guy suggested but then you should not have sound from the bottom speaker either. You can wiggle the connection after the sound goes out and listen for it to come back to check for a cold solder joint.
Other possibilities, if both speakers are out, swap the right and left inputs to the amp. Does the sound switch sides? If so it is a signal line problem in the player or the decoder. I have found the decoders to be loaded with cold solder joints but this is not work for amateurs. Check the door speaker connections. Check that the RCA plugs are firmly attached to the decoder board. Check the connections on the output transformers, are the tight? There are other things as well but this might help

You could have connector problems on the speaker crossover network located inside the amplifier compartment on the opposite wall from the amplifier. Typically the solder joints go bad where the connectors are soldered to the board. Usually a simple resoldering can fix it. There could also be problems with the connectors at that particular speaker itself.