Before mounting the SD card, make sure you have a ‘free’ directory where you want to mount the SD card. If you do not have such a mountpoint, you should create one. For example:
Plug in your SD card to the SD card reader of your pc or laptop and issue the following comand:
Copy the UUID (e.g., 6fcc-a123) of the device that refers to your SD card.
Now you can mount your SD card with the following command:
sudo mount -U 6fcc-a123 ~/mymountpoint
Beforce disconnecting your SD card, you should unmount it:
sudo umount ~/mymountpoint