Some states in this country allow for rights of non-parents of a minir to have some semblance of visitation rights with a minor child. I suggest that you consult with a family law attorney to see if your state of residence has a statute in place pertaining to an uncle. Most likely the answer is no. If the answer is yes, then the attorney can discuss your legal options.However, from what you have written, you seemingly need to iron out the problem with your sister. After all she is the parent of the child you want to see.