ok, so I think if it sees the device being plugged in, then it probably sees the card reader. You could try running lsusb to see all your USB devices, and lsblk -o NAME,FSTYPE,MOUNTPOINTS to see your block devices (disks), and see if it appears there also.

It still may not be able to actually read the file system even though it sees it as a disk. One reason for that could be it's not supported by your kernel. Do you know what file system the card is formatted with? If it appears in the lsblk output, it will say in the second column.

Edit: when I tested this with my own card reader, I see this output:

$ lsusb
Bus 002 Device 002: ID 0bda:0301 Realtek Semiconductor Corp. multicard reader

$ lsblk -o NAME,SIZE,TYPE,FSTYPE,MOUNTPOINTS
NAME         SIZE TYPE FSTYPE MOUNTPOINTS
sda          3.6T disk        
├─sda1        16M part        
└─sda2       3.6T part ext4   /mnt/disk2
sdb            0B disk        
sdc            0B disk        
sdd            0B disk        
sde            0B disk        

Each device (sda, sdb, sdc) is a physical disk. sda is my SSD. sdb, sdc, sdd, and sde are all "drives" from the multi-reader. Each type of card shows as its own, basically.

Now if I plug a card in, I get a little icon in the system tray (disk and devices) where I can mount and open it. And this has appeared in my lsblk output:

sdc         59.5G disk        
└─sdc1      59.5G part exfat  

That is a 64GB SD card formatted with exfat.