How do I get from Marriott Courtyard Sha Tin to Hong Kong Convention Center using subway?

From your hotel, you can walk to reach Shek Mun Station first and then take the Ma On Shan Line to reach Tai Wai Station.
Upon reaching the Tai Wai Station, you can change to Eas Rail Line to reach Hung Hom Station. Then you can change to West Rail Line to reach East Tsim Sha Tsui Station. There you can walk to the Tsim Sha Tsui Station to take the Tsuen Wan Line to reach Admiralty Station. There you can change to Island Line to reach Wan Chai Station. Get out of the station from Exit A1 or C, you can walk to reach the Convention Center easily.