Yes. I presume you have a login, so I guess you know how to make up recipes and save them. So you could do that if you had orange, carrot and kale juice on ND, by putting in the percentages or weights. But of course there is no Kale juice and only tinned carrot juice there.

I doubt you will find a site that has that kind of info or ability to calculate it on the web, because there are unlimited numbers of combinations of different ways to juice different fruits and veg. I think you will have to be lucky, good at maths and do a lot of web searching just to find an approximation for one complex juice.

Love to be proved wrong though... :)