I'm looking to build the following Shopping Cart Rule and I have no idea how to do it. I have multiple sku available, if you add 2 different sku in your cart from the same category, you get 10% off. It can be any combination of sku,any quantity , and the discount is only applied once.
I believe this configuration would work for you. You'll need to set your own categories, of course, but the format should work to qualify your discount for carts that contain 2 or more items from the target category(ies).
Now, if you only want the discount to apply to those qualifying products (and not the whole cart), then you will need to build a similar construct in the "Actions" panel so that the discount will only apply to products in the cart that match your criteria.