Got 2 veneers on my front teeth, there is a big white spot showing on one of them. Why is that and how can it be fixed? (photos)

When veneers are made very thin, sometimes they allow the color of the natural tooth or the cement to show through the thinnest parts.  It appears that the white "headlight" may be showing through the new veneer.  If the veneer is less than a week old and was dried out when the veneer was bonded, the appearance might dissipate as the tooth rehydrates.  If it is there after more than week, the veneer might need to be re-bonded or replaced.  Many veneers can be removed with an Erbium laser (called an er:YAG laser) that removes the cement without damaging the veneer.  Removing the veneer could allow your dentist to use a different color cement to change the whiteness you see.  If it's not possible to repair the show-through color of the veneer, it might need to be replaced entirely.  I would recommend talking with your dentist to discuss the options to make your front tooth look the way you want.
Best ~ Dr. Jason