Can I convert a mini guitar-amp into a portable auxiliary speaker?
You could try cutting the  bottom trace under the writing "C498" and then applying the input to the pin nearest "01v1" possibly through a 10K resistor. that will break the tone control, but the volume control should work.

This is the circuitry behind the volume control, so IC4 is probably the amplifier, 

also there's a small capacitorin that trace so it's power or amplifier output trace - that makes it look like an input.