The Nikon Z 6II features two memory card slots. One slot supports the extremely fast CFexpress Type B cards and also the slower XQD cards, whereas the other slot supports UHS-II SD/SDHC/SDXC cards.
The CFexpress 2.0 standard is supported but not the latest 4.0 standard. CFexpress 4.0 cards can still be used but you won't see any speed benefits in-camera.