What were hobbies that King George V enjoyed?

He enjoyed working on his stamp collection.

"George V was one of the notable philatelists of his day. In 1893, as the Duke of York, he was elected honorary vice-president of what became the Royal Philatelic Society of London. On his marriage that year, fellow members of the society gave him an album of nearly 1,500 postage stamps as a wedding present. He expanded the collection with a number of high-priced purchases of rare stamps and covers. His 1904 purchase of the Mauritius two pence blue for £1,450 set a new record for a single stamp. A courtier asked the prince if he had seen "that some damned fool had paid as much as £1,400 for one stamp". "Yes," George replied. "I was that damned fool!"' (Source: Wikipedia)

King George also enjoyed spending time with his family and his granddaughter, who is now the Queen of England!