You'll probably want to pass the card reader through to the guest. To do this, select the VM menu->Removable Devices->Sony card reader->Connect (Disconnect from Host). Then you'll need to mount the card in Linux, almost all recent distros will do this automatically when the card is inserted, but some will need some coaxing.
The standard command to mount any partition device will be:
mount (block device) (mount point)
The block device will normally be something like /dev/sdb1, but the actual name of the device will depend on hard drive configuration. You can check the contents of dmesg to be sure. Most multi card readers present a block device for each slot they have (they'll look like /dev/sdb without a number). You will of course need to be root to do that.
See "man mount" for full details on the mount command.
