Quite frankly, a skeleton playing a trumpet to be very implausible, if not, impossible. In order to understand this, it is necessary to understand how a trumpet is played.
The trumpet is played when the player inhales a sufficient supply of air, and forces that air through his/her lips, causing a vibration of the lips. The combination of air flow and lip vibration causes the sound to start in the mouthpiece of the trumpet. This, in turn, is amplified by that trumped itself, and the sound exits through the bell of the trumpet.
Skeletons, however, lack the muscle tissue and skin to provide lips to the mouthpiece of the trumpet. Even if they did, there would have to be a sort of air supply system to bring air to the lips for them to vibrate. Skeletons have none of these. It is impossible for the skeleton to play the trumpet.