we would normally talk about jewellery [ even if it's only one item] not a jewel
Yes, jewel in the singular refers to one stone "India was the jewel in the crown of the British Empire".
jewelry is spelled With 1 L in America
No, in the USA it is spelt 'jewelry', but in Canada, obviously also part of America, and some smaller English-speaking islands in the Carribbean etc., it is spelt 'jewellery'. There are 35, countries in America, not just the USA.
and only two Es