Pink dogwood chlorosis
We do not have enough information to answer your question. How old is the dogwood, where is it located, how do you care for it, etc.
There is no easy answer as you have to figure out why this is occurring in the first place. There may be several reasons such as trunk, root, insect damage, etc.
Look around the base of the root system. Is the tree planted too deeply, has there been damage to the trunk, mechanical damage to the root system, too much mulch, boring insects around the base of the trunk or in branches, etc.
Here is our dogwood publication for more information on signs and symptoms.
Look for the above issues and read the publication. You can submit photos of the whole tree, around the base of the tree, and/or affected foliage/ damaged areas on trunk with more information so we can see what you may be dealing with.