I see small black spots on my sisters tongue. What causes this and what will get it off. Thank you

If she smokes it is probably serious, if she smokes a lot its probably nicotine sticking to an unwashed tongue.

If she has black spot on her tongue sounds like she has poor mouth hygiene and if you saw them they are probably bothering her and she asked you to look, right ? That is really gross.

Okay, tell her to brush her tongue, it hurts, but it may help, gargle with an antispectic mouth wash, or 3% peroxide (l part peroxide to three parts water), or if that doesn't sound good to you two, then salt water, teaspoon to two parts water. She has to keep it in her mouth for at least a minute. See if all this helps then if the black spots don't go away she has to see a dental hygeinist. Good luck.

Is she currently on any antibiotics? This is a known cause of black spots on the tongue, which can lead to a condition known as "harry tongue." Info on this can be found here:

Black, hairy tongue: What causes it? - MayoClinic.com

Following the remedies outlined in the above post should clear this up.
I hope this helps.