Karyoplasma

They weigh about 1kg. The force of air is harder to answer as it’s less about how hard you blow and more about how loose or tight your lips are around the mouthpiece. But since dolphins can blow water several meters into the air, I’d just assume they can produce more than enough force to make a note.

No, needs to be 2. A dolphin’s windpipe is not connected to their mouth, so they couldn’t push air in 1.

They are called valves and not pushing any valves is called “playing open”. It just produces the trumpet’s harmonic series over its fundamental frequency, kinda like a bugle. Most trumpets are Bb trumpets, so dolphins could theoretically play all notes in that series. That’s very hard and requires excellent lip control, of course.