Good Morning,
A customer has asked for a wedding cake (3 tiers) with white chocolate shavings on the sides. I am lost and do not know how to make shavings. Can someone help? How do I make them? Can I make them ahead of time? How would I attach to the sides of the cakes? OM goodness, I'm lost.

For small shavings you can just run a veggie peeler over a block of white chocolate to make little curls/shaves.
You can also melt the choc. and pour it onto a flat surface (like the back of a baking pan) and then use a thin spatula or other tool to make curls/shavings while it is set but not hard.

You can surely make them ahead of time and store in a plastic container to use when you are ready, just like storing the chocolate itself, though these can break easier and have to be handled gently.

I shave mine onto parchment/waxed paper then lift the paper into the container so I never touch them with my hands (breaks and melts them)

Others may have other great emthods and tips too, these are just what I do. HTH