It looks like your tree is stressed from transplanting. Please make sure that you water your new tree regularly! Here is a link to an article from the University of Minnesota about watering new trees. 

Your tree has a fungal disease, most likely Septoria leafspot, but that is not surprising this time of the year. In fall, it’s common to see spotting and curling since the tree is already preparing to drop leaves.

From Rutgers, in New Jersey:

Leaf spots caused by the fungus Septoria were also common this year. Septoria leaf spot on dogwood is caused by Septoria cornicola. Septoria leaf spot in dogwood usually does not become severe until mid to late summer, but this may vary depending on spring weather conditions. Despite the dramatic appearance of this disease, the overall impact on plant health is minimal. Infected leaves stay on the tree, so despite the necrotic tissue, there is enough green tissue to produce adequate carbohydrate reserves to sustain the plants for the season. Remember that the health impact of a leaf spot on a deciduous tree or shrub is limited to one season. Damaged leaves drop in fall and the plant gets a reset for the following year.

Here is information on leafspots in general from UMN. 

This fall, make sure that you rake up and dispose of all the leaves to minimize the risk of fungal spores overwintering near your tree. Water at the roots--never splash water on the leaves. Don't fertilize until next spring, although I wouldn't necessarily recommend fertilizer for dogwoods in general. 

If you are really worried about the tree, you can apply a fungicide in the spring, but I don't think it's necessary. Keep the tree mulched and well-watered (but not too much!) for the first 1-3 years as it establishes and during drought thereafter. 

Based on your 3 photos, I don't think that you need to have the tree removed. Many of our trees and other plants get fungal diseases that we deem unsightly, but do not damage the plant. If you are concerned, you can talk to the company about the tree and make sure they they have a warranty/guarantee for 1-3 years. 

I would also recommend making sure they did not plant the tree too deeply. Most contractors plant too deep and cover the tree's root flare. Here is a publication on how to plant a tree so you can see if it was done well.