If you don't use the Octopus card, the charge is 37 Hong Kong dollars.
In fact, the subway can't go to Luohu from Sham Shui Po. You should change to the Kowloon-Canton Railway at Kowloon Tong Station, and then go to Lo Wu from Kowloon Tong. So this fee is divided into two parts. The fare from Sham Shui Po to Kowloon Tong is HK$ 4 (Octopus 3.8 yuan), and the fare from Kowloon Tong to Luohu is HK$ 33.