Can a leopard kill a jaguar?

Depends on what you mean by "can".

Big thing IRL is that jaguars live in South America and Leopards live in Africa and Asia.

Different continents, They wouldn't meet under natural conditions.

If they should meet, in a zoo or something:

The average jaguar is bigger than the average leopard. But they're so evenly matched that it'd take something real special for the animals to fight each other. Even the Winner would most likely be hurt.