Hello, XXXXX
It sounds as though your kitty may have an upper respiratory infection (URI).
What you can do at home to help him feel better is keep the nose and eyes clean of any discharge. You can use warm water dampened cotton balls or Qtips to do this. You can also bring him in the bathroom when you shower. This will allow the steam to help break any congestion in the head and chest if he sounds stuffy. A vaporizer can well too for this. You can give him a 1/4 tablet of Chlor-Trimeton every 12 hours for sneezing
You can get Chlor-Trimeton at any drug store. It is next to medications like benadryl.
If it does not get better in 7 days after starting the OTC medication, you will need to get an antibiotic from your vet to clear it properly. Sometimes if URIs are left untreated they can cause eye ulcers or even pneumonia.
Dental issues can also cause sneezing, so watch his eating habits. Usually when dental problems happen, eating will come to a near stop.
Please let me know if you need further assistance with this.
Sincerely,
Micki
Expert in cat behavior and health
Expert in cat medical and behavior issues.