jQuery URL/undefined 404 error

Hi, I'm using the Rock Star Theme on my Site. I'm getting a 404 "Failed to load resource: the server responded with a status of 404 ()" "https://www.giveaway-partyband.de/booking/undefined" error on each view in the Chrome console. I think this happens due to a fail in the jQuery Code. Can anybody help me? Does anyone else know that? Thanks.