select game object triggers GUI

I have my level to a point where I can select an object with a click or touch and it will trigger my GUI buttons to appear. From there the user can make a selection. The selection the user will need to make will be to identify the object they have just clicked that triggered the GUI. The GUI buttons should include several wrong options and only one correct answer (the object they chose to trigger the GUI).

Does anyone have an idea of how to approach this?

OnMouseDown() is a function that fires when you click on an object(that has a collider)
so you can attach a script to your object that has this OnMouseDown() function that enables the OnGUI() that displays a menu on the screen.
or search for “onmouse” for more options on mouse interaction with objects.