The Leica D-Lux 8 features a single memory card slot that is compatible with SD/SDHC/SDXC (UHS-II) memory cards. It's also backwards compatible with the slower UHS-I cards.
For shooting video at 4K 30 p / 100 Mbps you will want a card that has a minimum video speed rating of V30 / U3, although a card with a V60 or V90 video rating will run cooler and also help you to offload the files to your computer faster.
It's always a good idea to format a new memory card before use. Just select the "Format Storage" option from the Menu and then confirm the action.