Overall the canopy of the dogwood does not look bad. We notice some branch dieback (flagging) where cicada eggs were laid.  No action is necessary. Dead branches that you can reach safely can be pruned out at any time if desired. 

The discolored leaves and spots on the foliage are symptoms of several fungal diseases such as spot anthracnose and powdery mildew.  Some dogwood varieties can be more susceptible to these diseases than others.  We notice some spot anthracnose on the foliage which is very minor. It is not usually a big problem, but we're seeing a lot of it this year because weather conditions were perfect for it. Since disease severity is sporadic depending on how wet the spring season is routine fungicide applications are not recommended. https://extension.umd.edu/resource/elsinoe-leaf-spot-dogwood

Powdery mildew - Older infected leaves often develop purple blotches that progress to dead areas. There is a range of susceptibility among dogwood to powdery mildew. The best recommendation is to plant powdery mildew resistant varieties in the future. Pruning for air circulation may help. You will have to monitor the plant in the future and decide if you want to spray fungicides or horticultural oil products listed for powdery mildew. This disease does not kill the plant but can weaken it. https://extension.umd.edu/resource/powdery-mildew-disease-trees-and-shrubs

Dogwood is a native understory tree and grows best in morning sun and afternoon shade in a moist, well-drained soil. They are not tolerant of full sun, hot and dry, poorly drained sites, or flooding. If the dogwood is in full sun, it will need moisture during dry periods. 

Here are our pages and additional links on How to Grow Dogwood. You can look for resistant varieties to both diseases in the future.  https://extension.umd.edu/resource/diagnose-dogwood-problems-chart

https://extension.umd.edu/resource/how-grow-dogwood

If you notice additional symptoms, you can send more photos.

Marian