How to Mount EXFAT partition on Ubuntu 16.04 LTS
$ sudo apt-get install exfat-fuse exfat-utils
If you need to mount it from the command line, you could do
$ sudo mkdir /media/exfat
$ sudo mount -t exfat /dev/sdxx /media/exfat
where /dev/sdxx could be /dev/sda1 or /dev/sda2, or so on.
If you are not sure whether the exfat partition you are looking for is /dev/sda1 or /dev/sda2, then you could also run
$ sudo lsblk -o NAME,FSTYPE,SIZE,MOUNTPOINT,LABEL
The ghome-disks utility can also be used to start and mount this. Since it is /dev/mmc and not /dev/sd, the system will probably have it assumed to be system owned, and will mount under root ownership only.
You can follow the above, but will then have to do a lot of crap with permissions to the mount. If it were or is a fixed mount and not the automount /media mechanism one can do that once. However it will be reset on every mount and be inconvenient.
Solution might be to use gnome-disks. That has a problem however. The FUSE exfat driver and the above asset is root owned. Gnome-disks will not access and mount it due to the system ownership problem
So use a utility to run gnome kit stuff from a command line as su root.
apt-get -y install gksu
installs the gksudo and other stuff.
gksudo gnome-disks will mount the device and make it properly available.
Note that sudo gnome-disks makes the thing root owned again, since you are running as root user in the desktop. gksudo will run as root, but effectivly as the user desktop user id.