how to execute a command after resume from suspend?

You can place your scripts in the /etc/pm/sleep.d directory to have them run after suspend. You will need to add a conditional to make your script run only during resume and not during the suspend process as well. For example, your touchpad script would look like:

case "${1}" in
    resume|thaw)
        DISPLAY=:0.0 ; export DISPLAY
        xinput set-int-prop "SynPS/2 Synaptics TouchPad" "Two-Finger Scrolling" 8 1
        xinput set-int-prop "SynPS/2 Synaptics TouchPad" "Synaptics Two-Finger Scrolling" 8 1 1
        xinput set-int-prop "SynPS/2 Synaptics TouchPad" "Synaptics Two-Finger Pressure" 32 10
        xinput set-int-prop "SynPS/2 Synaptics TouchPad" "Synaptics Two-Finger Width" 32 8
        setxkbmap -layout gb
        xkbset m
        xkbset exp =m
        su $USER -c "sleep 3; /usr/bin/xmodmap -e "keycode 135 = Pointer_Button2"" &
;;
esac

Be sure your script is marked globally executable and change $USER to the corresponding username.

You can find more detailed information in the pm-suspend manpage (man pm-suspend) or by looking at the documentation in /usr/share/doc/pm-utils (particularly /usr/share/doc/pm-utils/HOWTO.hooks.gz).

On Ubuntu 16.04 I had to create service this way:

1. create file

   sudo gedit /etc/systemd/system/somename.service
   

2. put inside

   [Unit]
   Description=Some description
   Before=sleep.target
   StopWhenUnneeded=yes
   
   [Service]
   Type=oneshot
   RemainAfterExit=yes
   ExecStop=-/path/to/your/script.sh
   
   [Install]
   WantedBy=sleep.target
   

3. enable service

   sudo systemctl enable somename
   

4. (optional) if not working after resume from suspend > check for errors with

   journalctl -u somename.service
   

Open this file:

sudo vim /lib/systemd/system-sleep/hdparm

Contents:

#!/bin/sh

case $1 in 
  post)
    /usr/lib/pm-utils/power.d/95hdparm-apm resume
    ## Paste your command to run your script
    ;; esac

Your command will execute with admin privileges.