Ein Fundstück zum Thema :
... I would probably use the name of the profession after "with", the location after "at", and I would use "on" for websites.
I have to register with a doctor.
I have to register with a dentist.
I want to register with a massage therapist.
I am going to register at the university.
I am going to register at the doctor's surgery.
I want to register at the massage therapy centre.
I have registered on the Expedia website.
I'm going to register on the Hotmail site.
... to be confirmed ... :-)
Ich wünsch' Dir Frohe Feiertage und einen Guten Rutsch !