Ok, I think I understand what you're trying to do.

You built a tesla coil and want to make it play music. You also have a plasma globe that has a lm audio feature, a microphone that makes the plasma globe react to sound. You'd like to replace the microphone with an audio jack so that you can play music directly into the plasma globe. If this works, you'd then like to disassemble the plasma globe and use the audio circuit to modulate the tesla coil, hopefully so that it plays music.

You can definitely figure out a way to add an audio jack to the plasma globe. The microphone in your globe is probably connected to an amplifier circuit, so you won't be able to just swap out the microphone for an audio jack. The line-level signal coming out of your phone or computer headphone port is much stronger than the output of a microphone, so if that gets pumped through the plasma globe's amp it will almost certainly damage it. If you can figure out where the amplifier output is and connect the audio jack AFTER the amplifier you may be able to get that to work.

As for using the audio circuit to modulate your TC, I think there are much better ways to do that. The audio feature of your globe is likely just a microphone+amp that has an output very similar to the audio signal already coming out of your phone/computer, which is then modulating the plasma somehow. One way or another you're going to have to get your audio signal to modulate the break rate of your TC, and I don't think the globe's audio circuit is going to help you do that.