can you paint over gloss with egg shell paint without rubbing it down and applying primer first
You could have adhesion problems if the gloss surface has fully cured and you should take the time to de-gloss it a bit. It really will not take you that long to add tooth to the surface with some fine grit sandpaper. Of course you want to clean the surface thorougly.
Whether you need to prime depends on what shape the surface is in, colors you are using and so forth. Use good paint store, not box store, paint for sure.
I still used primers to be safe when switching from oil to latex and acrylics but you may not have to do so. I would for sure if you happened to be painting oil over acrylic but in this day and age that is unlikely to be happening. A primer coat is helpful making dramatic color changes.