Currently, there are no trains running from Wuhan to HK directly. So, you could consider transferring at Guangzhou. There are multi trains departing from Wuchang Railway Station of Wuhan to Guangzhou everyday. When you arrive in Guangzhou, you could take a train from Guangzhou East Railway Station to reach HK in 2 hours.
For the train schedule and ticket fare, please refer to China Train Schedule(https://www.travelchinaguide.com/china-trains/)