Hi @ag9
Having Adobe Target implemented does not natively include the ability to trigger a lightbox pop-up, you would need to implement a 3rd Party Library (plenty available if you google) to enable lightbox pop-up functionality - assuming your website doesn't have this functionality already.
You could then use Target to load the lightbox library and trigger a lightbox pop-up, this would typically be an XT or A/B depending on your requirements.