Your tree appears to be in decline, but there are no disease or insects that cause problems visible on this tree. That suggests an environmental problem.
You can prune out the dead branches and be sure to water during droughts.
You can also send us photos of the base of the tree, which may give us more clues about the problem.
Here are some reasons why trees decline: https://extension.umd.edu/hgic/topics/tree-and-shrub-problems-not-caused-disease-or-insects-abiotic
We don't see an obvious problem from the base photo.
Dogwoods are forest understory or edge trees. They are adapted to part to full shade. This looks like a sunny location. It may be too hot and dry for it to be happy for an extended time here.
Another possible problem could be the fungal disease powdery mildew, which isn't infecting leaves yet. It will show up later in spring if your tree is susceptible to it. This can be a yearly problem and will slowly weaken a tree. Here's more about it: https://extension.umd.edu/hgic/topics/powdery-mildew-trees-and-shrubs
There are new varieties of dogwood that have been bred to be resistant to powdery mildew and if you replace this one, that's the way to go. The link above gives some ones to buy.