How do you know if you have enough Vitamin B12 as a vegetarian?
You need to get a blood test at the Doctor's office. The symptoms are weakness in the body, Anemia. numbness in arms and legs, and shakiness.
It is not possible to know that you have enough Vitamin B12 as a vegan. However, you should make sure that your diet contains this daily in order to get full benefits. Get detailed information on http://www.vegansociety.com/lifestyle/nutrition/b12.aspx and http://www.webmd.com/food-recipes/news/20030618/vegetarian-diet-b12-deficiency.
When I was a vegetarian, I just took a supplement for B12. You will probably fall low without that.