There are two vitamins not found naturally in plant foods⎯vitamin D and vitamin B12. Vitamin D is obtained via the sun. Not all people need to supplement with vitamin D. You can learn more about that topic in my article - Vitamin D: To Supplement or Not To Supplement?
Vitamin B12 is also absent from plant foods, at least unprocessed plant foods. It is only found in animal products such as meat, seafood, dairy products, and eggs.1There are many plant-based (vegan) food items which are fortified with B12⎯cereals, non-dairy milks, meat substitutes, and so forth. However, these usually come in the form of a package with many other not-so-healthy ingredients in them so they're not always the best choice.
So who cares about vitamin B12? Why make such a big deal out of it?