the speaker is normally driven via a pnp transistor and an 82R resistor, so you should be ok to test it with a 100R resistor in series with the speaker and a 5v supply. You should leave one end of the resistor / speaker free, and just dab it on the supply - you should hear crackling sound.
The other way would be to test the speaker in the QL itself - the speaker connects into a push type connector which holds the wires in place, pulling up the connector releases the wires.