Supposing someone got poked with a drug needle , like in a finger, what would it look like and would it heal?

Depends on size: frequently there is no external obvious sign of the needle unless it was a large needle. Amazingly I have seen lots of broken needles in patients that are not always painful especially diabetics. In the finger I presume one would have pain from the needle but certainly the puncture wound would heal if the needle was not terribly dirty otherwise if contaminated the area would be reddened