'Do you want any cake?' This is using the word in its uncountable form. This is the most usual way to ask this question. It could mean that you have one large cake and you are offering a slice. It could also mean that there are various different cakes. 'Do you want a cake?' This is countable singular. There is one cake and you are offering the whole cake to someone, or there are several cakes and you're inviting the person to choose just one. 'Do you want any cakes?' There are a lot of cakes, and you are inviting the other person to take several of them.

Thanks!

Depending on the context, 1) "Do you want any cake" , means that you only have a cake; while 2) "Do you want any cakes" , means that you have a few cakes to choose from.