Q.What Is Wrong With This Plant?
This had been on the plant for a couple of years but has got a lot worse and is killing the new growth

Certified GKH Gardening Expert
These articles should help:
https://www.gardeningknowhow.com/plant-problems/disease/plant-leaf-spots.htm
https://www.gardeningknowhow.com/plant-problems/disease/bacterial-leaf-spot.htm
https://www.gardeningknowhow.com/ornamental/shrubs/boxwood/controlling-boxwood-insects.htm
https://www.gardeningknowhow.com/ornamental/shrubs/euonymus/euonymus-scale-treatment.htm