How to get Touch Position on screen
  1. New C++ class inherit from GameViewportClient

  2. Project Settings -> Engine -> General Settings -> Default Classes -> set Game Viewport Client Class as your customized class.

  3. Override function InputTouch

    virtual bool InputTouch(FViewport* Viewport, int32 ControllerId, 
    uint32 Handle, ETouchType::Type Type, const FVector2D& TouchLocation, 
    float Force, FDateTime DeviceTimestamp, uint32 TouchpadIndex) override;

    Argument TouchLocation is the Touch Position.

Mobile Input - Swipe and Pinch

A plugin for Unreal Engine 4 that exposes touches and swipes on mobile devices as events in blueprints

Ultimate Touch Components