Answer
The answer is Wimbledon. Gabriela Dabrowski has yet to capture a Grand Slam title at Wimbledon. She came close in 2019 when she reached the semifinals with Xu Yifan, but they were defeated by the eventual champions Hsieh Su-wei and Barbora Strýcová. However, she has experienced success at the other three Grand Slams; winning the Australian Open and French Open titles, and reaching the US Open final twice.