There are two shooting options in Hitman Sniper.

Option 1 - Shoot Button:
Note: The shoot button option must be set to "ON" in the in game settings menu. (From in game, tap the Pause menu at the top left corner of the screen > Locate the SHOOT BUTTON option > Tap the red arrow buttons to toggle the option to ON)

With the shoot button activated the player must enter the Scope view with the rifle by tapping anywhere on the screen while in game. Once the player is looking through the weapons optics, shoot by tapping the shoot button that appears at the bottom left hand side of the screen (bottom right hand side of the screen for players playing with Left Handed mode activated)

Option 2 - No Shoot Button:
Note: The shoot button option must be set to "OFF" in the in game settings menu. (From in game, tap the Pause menu at the top left corner of the screen > Locate the SHOOT BUTTON option > Tap the red arrow buttons to toggle the option to OFF)

Tap anywhere on screen while in game to look through the rifles scope. Once the player is looking through the rifles optics, shoot by tapping anywhere inside the scopes view.