Two-finger scrolling not working since ubuntu 17.10+ [duplicate]

The answer here by @hpotter40 worked for me:

$ sudo modprobe -r psmouse
$ sudo modprobe psmouse

This was taken from comment #16 of this bug report: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1722478/comments/16

Update for a more persistent solution:

Based on comment #44 and #45 of the same bug report above, this should also work. Open the file /etc/default/grub and edit the value of the GRUB_CMDLINE_LINUX_DEFAULT variable. By default this has the value of "quiet splash". The value "psmouse.synaptics_intertouch=0" could be added to it so that it becomes like:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash psmouse.synaptics_intertouch=0"

Then update GRUB by executing:

$ sudo update-grub

Reboot your system and this setting should survive even after suspends. As a note, all these answers are simply workarounds until the kernel error could be identified and patched.

You can enable two finger scroll by clicking System Settings > Mouse & Touchpad. You will see a window like this

You can (un)check the check box according to your preference.