Configure

To enable touchpad:

$ doas mkdir /etc/X11/xorg.conf.d
$ doas cp /usr/X11R6/share/X11/xorg.conf.d/70-synaptics.conf /etc/X11/xorg.conf.d/

Add this section to the top of /etc/X11/xorg.conf.d/70-synaptics.conf:

Section "InputClass"
        Identifier "touchpad catchall"
        Driver "synaptics"
        MatchIsTouchpad "on"
#        MatchDevicePath "/dev/input/event*"
		Option "TapButton1" "1"
		Option "TapButton2" "2"
		Option "TapButton3" "3"
	Option "VertEdgeScroll" "on"
	Option "HorizEdgeScroll" "on"
EndSection

Here is a sample full config:

# Example xorg.conf.d snippet that assigns the touchpad driver
# to all touchpads. See xorg.conf.d(5) for more information on
# InputClass.
# DO NOT EDIT THIS FILE, your distribution will likely overwrite
# it when updating. Copy (and rename) this file into
# /etc/X11/xorg.conf.d first.
# Additional options may be added in the form of
#   Option "OptionName" "value"
#
#Section "InputClass"
#        Identifier "touchpad catchall"
#        Driver "synaptics"
#        MatchIsTouchpad "on"
## This option is recommend on all Linux systems using evdev, but cannot be
## enabled by default. See the following link for details:
## http://who-t.blogspot.com/2010/11/how-to-ignore-configuration-errors.html
##       MatchDevicePath "/dev/input/event*"
#EndSection

Section "InputClass"
        Identifier "touchpad catchall"
        Driver "synaptics"
        MatchIsTouchpad "on"
#        MatchDevicePath "/dev/input/event*"
		Option "TapButton1" "1"
		Option "TapButton2" "2"
		Option "TapButton3" "3"
	Option "VertEdgeScroll" "on"
	Option "HorizEdgeScroll" "on"
EndSection

Section "InputClass"
        Identifier "touchpad ignore duplicates"
        MatchIsTouchpad "on"
        MatchOS "Linux"
        MatchDevicePath "/dev/input/mouse*"
        Option "Ignore" "on"
EndSection

# This option enables the bottom right corner to be a right button on clickpads
# and the right and middle top areas to be right / middle buttons on clickpads
# with a top button area.
# This option is only interpreted by clickpads.
Section "InputClass"
        Identifier "Default clickpad buttons"
        MatchDriver "synaptics"
        Option "SoftButtonAreas" "50% 0 82% 0 0 0 0 0"
        Option "SecondarySoftButtonAreas" "58% 0 0 15% 42% 58% 0 15%"
EndSection

# This option disables software buttons on Apple touchpads.
# This option is only interpreted by clickpads.
Section "InputClass"
        Identifier "Disable clickpad buttons on Apple touchpads"
        MatchProduct "Apple|bcm5974"
        MatchDriver "synaptics"
        Option "SoftButtonAreas" "0 0 0 0 0 0 0 0"
EndSection

Restart openbsd and changes should apply.