Q.What Is Happening To My Brugmansia?
I moved it into the sun for a day to see if it would enjoy that. Then I saw something weird on the leaves (see image). Is this a reaction to the sun? I’ve never seen this.

Certified GKH Gardening Expert
I think this is a compounded issue. I see what looks like the signs of spider mites. Those little speckles on the leaves are usually a good sign, as well as the wrinkling of leaves. The sudden sun exposure may have made this worse.
Treat the mites with something like neem oil or its extract, azadirachtin.
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/azadirachtin-vs-neem-oil.htm
https://www.gardeningknowhow.com/plant-problems/pests/insects/spider-mite-control.htm
As far introducing to the sunlight- This should be done, gradually. Once you treat for mites, then you can start to introduce it back to the sun a few hours a day, increasing the time each day.
https://www.gardeningknowhow.com/ornamental/trees/brugmansia/growing-brugmansias-in-containers.htm