If you want to be able to listen to music while you are in the shower there are a few obvious solutions, but there are also a few things you need to avoid.
The easiest solution is just to bring a portable stereo into the bathroom and place it somewhere dry and away from moisture and water.
Some people may consider bringing a laptop into the bathroom and using that as a sound player for their showers. At first, this sounds like a feasible idea: it’s portable, it has music software on it, and it contains your favorite playlists already. But consider that a laptop is cooled by fans which blow outside air into the case, and the bathroom gets steamy when you take a shower, so you will essentially have a laptop that is blowing moisture into itself which can result in damaged electronics.
The other option that hopefully no one will try is installing non-waterproof speakers in a shower. Again, this is a horrible idea because water will get into the speakers electronics and the speakers will be damaged and at worst you could be electrocuted.
If you want shower speakers, you must get speakers that are specifically designed for that purpose. The speakers need to be waterproof and intended for being used in a shower.