The census page that you linked tells you that you must look in the parish church records for Horg parish, Støren district, Sør-Trøndelag. The census also lists a birth date of 24 May 1903 so you would expect the baptism to have been performed a few days to a few weeks after that birth -- this is assuming the family were members of the Norwegian Lutheran church.
The Digitalarkivet web site has been adding scanned images of the original Norwegian parish church records for anyone with Internet access since November 2005.
The Digitalarkivet web site - http://digitalarkivet.uib.no/cgi-win/WebFront.exe?slag=vis&a...
An English option is available by clicking on that word from either the left hand column or the blue link bar along the bottom of the homepage.
The scanned images are available from the homepage link "Skanna kyrkjebøker" [Norwegian version]/"Digitised parish records" [English version] which is listed along the left hand column and from the blue banner of links along the top section of the homepage.
Clicking on "Skanna kyrkjebøker" [Norwegian version]/"Digitised parish records" [English version] will bring up another screen and listing to choose from. Choose "Lesa skanna kyrkjebøker" [Norwegian version]/"Read the digitised parish records" [English version].
After you've clicked on that link and a new main page has presented on the screen be sure and read the instructions that are available from the Digitalarkivet for navigating the scanned records. The instructions are available in Bokmål (official Norwegian), Nyorsk (Norwegian), Davvisámegiella (Saami), and English.
Recommended basic reading are the "Startsiden" [Norwegian version]/"Main page" [English version], "Brukerveiledning" [Norwegian version]/"User's guide" [English version] and "Om tjenesten" [Norwegian version]/"About this service" [English version].
Good information about translating the formats of Norwegian parish church records during various time periods, many of the basic terms used and understanding how to use the information should be studied at this web site -http://homepages.rootsweb.com/~norway/na20.html