There are several ways to connect to the PS4. To give you a specific answer I would need to know how you have things connected. The touchpad is definitely the most problematic feature of the PS4.
If you are directly connected to the PS4 and have the Quadstick booting with "Enable boot in PS4 mode" turned on (or ordered your Quadstick with PS4 as the default console), then look at
this configuration file for an example of pressing the touchpad and touching it at a specific location.
If you are using a CronusMax, then there are two possibilities: If "Enable boot in PS4 mode" is turned on, then the same method as above will work. If "Enable boot in PS4 mode" is turned off, then the CronusMax must be running the PS4 Crossover Essentials gamepack and the "select" button is remapped to press the touchpad. The position on the touchpad is controlled by the Right Analog stick. See
this configuration for an example. You will need to read the
instructions for the gamepack.
If you are using the Quadstick Manager Program and the CronusMax via the PCPROG port, then the Escape key is mapped to press the touchpad. See
this configuration for an example.