You should search for uinput and evdev. If you can get a list of touch events from someone with a real device, using evemu-record, you can replay them with evemu-play. See Understanding evdev to see how you can log absolute x and y events from a touchscreen device, such as EV_ABS / ABS_X, EV_ABS / ABS_Y and a touch such as EV_KEY / BTN_TOOL_FINGER. You can put these in a file, edit them and add your own, and replay the result with evemu-play, or send one event with evemu-event.

This too-detailed pdf, The Linux input driver subsystem may help you recognise some of the events you need to emulate.

You should search for uinput and evdev with evtest. If you can get a list of touch events from someone with a real device, using evemu-record, you can replay them with evemu-play. See Understanding evdev to see how you can log absolute x and y events from a touchscreen device, such as EV_ABS / ABS_X, EV_ABS / ABS_Y and a touch such as EV_KEY / BTN_TOOL_FINGER. You can put these in a file, edit them and add your own, and replay the result with evemu-play, or send one event with evemu-event. There are C and Python api's to create UInput devices and send events through them (tutorial).

This too-detailed pdf, The Linux input driver subsystem may help you recognise some of the events you need to emulate.