The first and most important thing to do when identifying a Nike shirt, is looking at the style code. Look for a small white tag with some numbers on it, inside of the shirt. On most (newer) Nike shirts, this label sits at the back of the large washing labels.
You should use the 2nd code from below and type this into Google or another search engine. This Nike number has the following template on newer shirts: XXXXXX-XXX. When you search for this code in Google and go to images, you should see the particular shirt if it's original, listed by trusted sellers, not from China. The shirt is 100% fake if you see different shirts or only images from Chinese/Asian sellers.