If you want to create a wiki about a topic that has already been taken, you can't. If you want to create a wiki about a topic has not yet been taken but has the same name as something else (let's say Dungeons in games and Dungeons in medieval times), you will now need to specify it in the wiki name/url
If you make a wiki about a topic that already exists, then it is called duplicating. You can make a wiki but your duplicated wiki has a very HIGH chance of getting reported as a duplicated wiki when you advertise your wiki on different wikis. People can report your duplicated wiki and your duplicated wiki will get closed.