As far as I know, even those with pernicious anemia absorb some B12, if taken orally in amounts of 1 mg or more per day. If your B12 levels are very low however, the preferred way is to initially boost up the levels with shots and then take orally high B12 doses to maintain the level. The preferred form of B12 is methylcobalamin as it can be more easily utilized than cyanocobalamin by the body (less conversion involved).
You can see how much your body is able to use B12 by having a bloodtest. The blood test doesn't actually tell you however, what is the status in your brains, and what its impact is on e.g. the thyroid hormones. For some people like me, B12 had a really powerful effect on the mood and the thyroid, despite the blood levels were "normal". This means that blood tests are useful only for telling extreme cases, and to see if you absorb well B12, but not much else.