How to find out if your fabric is made with nylon?

So I received a communion dress from a friend so that I can dye it into another color but I found out that the dye cannot dye any fabric that is with nylon. My friend and I do not know if the fabric consist out of nylon or not, because it looks and feels like cotton but my mom said it’s not really cotton so I have no idea.

So how can we find out(at home) if the fabric is mixed with nylon or not?