For a simple solution you could try making a copy of the waveform and then animate a vectical slit to move across the screen and use it as a track matte for the copy, essentially slicing a little section of the waveform to generate the "point". It may look just fine for your purposes.
I like this idea! A couple of linear wipes (offset from one another with an expression for ease of use) would get you a tiny slice. You could then apply blurs and/or glow effects to make a little dot traveling along the line.
- The Great Szalam
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