To mount exfat partition on Ubuntu, simply install the necessary packages:
$ 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