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%25 0 82%25 0 0 0 0 0"
            Option "SecondarySoftButtonAreas" "58%25 0 0 15%25 42%25 58%25 0 15%25"
    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.