For zoos I've been to since I started keeping track:
Giraffe-Only Exhibit: Roger Williams Park Zoo, Buffalo Zoo, Southwicks Zoo, Philadelphia Zoo, The Wild Animal Park, Cleveland Metroparks Zoo
Multi-Species Exhibit: Franklin Park Zoo, Disney's Animal Kingdom, Disney's Animal Kingdom Lodge, Elmwood Park Zoo
So 60% of the zoos I've been to with giraffes keep them alone, with only 40% mixing them with other species. One thing to note, it's interesting just how many of the zoos I've visited have giraffes in their collection. I've only been to 23 facilities since I started keeping track, so that's about 43% of them keeping giraffes. May not seem like a lot, but if I exclude aquariums and specialist facilities, it becomes 10 of the 16 zoos keeping giraffes, or 62.5%. There's a lot of talk on zoochat about the prevalence of meerkats, red pandas, etc. in zoos, but not about just how many zoos are keeping (usually generic) giraffes.