Can you attach a Baghdad battery to a flashlight?

You insert them.

Solar flashlights use light from the sun to power themselves. So unless it is a lunar powered solar flashlight{ using light from the moon to power itself}, or it stores power it takes in from the...

zinc

The battery ... without that it can't be a flashlight.

To attach a bulb to a battery you have to use a lamp holder. Connect the lamp holder to the battery and then screw the bulb into the lamp holder.