Can a crack on back of veneer be repaired?

it is highly likely that you will need to have the veneer replaced if there is a crack in it.  I recommend calling your dentist and have them take a look.  

Hello there,A new dental veneer should not be cracked.  I would recommend returning to your dentist for a complete evaluation.  If your veneer has a crack in it, the best option would be to replace it. Patching the veneer is not a long term solution. Good luck and I hope this helps. Follow me if you have more questions.Sarah Thompson, DMDSt. Louis, MO area (O'Fallon, IL)Real Self 100

Visit your dentist as soon as possible to evaluate.  This is not something that will go away.  Have it looked at properly and addressed.

New veneers shouldn't crack. I suggest visiting your dentist and letting them look at the crack. It may be necessary to replace the veneer. Patching a new veneer isn't the best option for the long term.