Ihave black spots under my tongue and I smoke also but not heavely very quit so should I do should I show this to a doctor or what test should I do?

See your doctor. I think your idea to see your doctor isa good one. He/she will be able to get a good look at them and biopsy them if necessary.
See an oral surgeon. After examining your lesions, you will be told what they might be and if further tests are indicated. They may or may not be related to your smoking, and if they were, quitting will not make them disappear.