Can't mount NTFS on Arch Linux

Your issue is that you haven't rebooted since upgrading your kernel, so you cannot load any of the kernel modules you require.

Always check the Arch documentation because it is usually the most updated source: https://wiki.archlinux.org/index.php/NTFS
As you can see it points you to the ntfs-3g package

So the first step to have a full ntfs support on linux is to have the above package installed. As root, simply install with:

pacman -Syu 
pacman -S ntfs-3g

After that you are ready to create/mount/read/write ntfs partitions.

Details:

pacman will take care of the dependencies (including fuse2). You don't need to recompile the kernel.

Once you installed ntfs-3g simply using the mount command should work. You could also use your file manager (Nautilus in Gnome or Dolphin in KDE, for ex., both support it and you don't need to manually mount anything)

I'm assuming it's an internal harddrive and not an usb drive due to the naming (sda), so if you want it mounted at system boot, you may want to put it in the /etc/fstab:

# <file system>   <dir>     <type>    <options>             <dump>  <pass>
/dev/NTFS-part  /mnt/win  ntfs-3g   defaults          0       0

Where according to your question, NTFS-part should be /dev/sda8, but please verify this.

Also, if you wish to write you might want to set the default recommended options:

# <file system>   <dir>     <type>    <options>             <dump>  <pass>
/dev/NTFS-part  /mnt/win  ntfs-3g   uid=username,gid=users,umask=0022    0       0

Here you should replace username in the uid field with yours. The umask setting should take care of the permissions compatibility between NTFS and Linux. The gid allows the members of the users group access (and mount). By default in Arch Linux every user is member of the users group. Check it with the groups command to see your membership.

There are a few other settings to take into account, but I will refer you to the official Arch Linux NTFS wiki for those.

Edit: added y to pacman flags, to make sure the DB is up to date before installing the package.

Edit 2: added u to pacman flag just in case someone already has the package installed and by chance there is an upgrade for that specific package and also dependencies that would break the system according to the comment made below. The downvote is a bit extreme considering the question/answer conditions of a new install.

Edit 3: Separated the update/upgrade from the install, just to be clear.