can you please give details of travel by train from hong kong to Xianyang and return?

Actually, no direct train can take you for this journey. You can take a train to Guangzhou first. Then at Guangzhou South Railway Station, you can take a direct high-speed train to reach Xian North Railway Station. Upon your arrival, you can take a taxi to Xianyang, spending about CNY100-120. For the return journey, you can also use the same mean by train.

To save time, you can also take the direct flight between HK and Xian. You will reach Xian International Airport and then take the airport shuttle bus to reach Xianyang Rainbow Hotel and then take taxi to reach anywhere you want to go in that place.