We do not see any concerning symptoms in the photo. If you are referring to the little bit of leaf yellowing, that may be due to cicada egg-laying damage and is rarely problematic. Look on the twig for a dashed-line scar in the bark, and if found, you can trim the twig off just behind this point where it next meets a joint with another twig.

If you do not see cicada damage, this may be the beginnings of minor leaf shed due to low-grade stress the tree is experiencing. Kousa Dogwoods are pretty resilient for a dogwood and not very prone to various pests or diseases, but as with other tree types, stressed trees do have increased vulnerabilities. Check the soil around its root zone at about six inches deep for moisture levels and irrigate it periodically if drying. Keep mulch from touching the trunk base and make sure the trunk isn't hit by lawn mowers or weed-whackers if it's immediately surrounded by lawn.

Leaves yellowed from stress won't turn green again and may shed early, even if the stress abates, but so long as the symptoms don't worsen or involve entire branches of foliage, it shouldn't be a concern.

Miri