Thats what I was thinking. Well you learn from your mistakes!!! Doesnt show up when i put a lens on though????
Sorry, but what is that picture trying to convey? It surely doesn't look like a sensor to me. It looks like a picture of the focusing screen IMHO. Or perhaps a picture of the mirror reflecting the focusing screen.
If there's some dust or lint on the focusing screen that's easy to clean, but if you got that stuff (or some liquid) stuck behind the screen (between the screen and the prism) that's gonna need either steady hands, or a trip to Nikon, or better still, just leave it in there, because it doesn't affect anything.
And by the way never ever touch the reflex mirror with anything. Unlike regular looking glass this one has the silver coating on the
top side of the mirror and it is extremely delicate. Doesn't matter if there's dust on the mirror, since it does not participate in the picture taking.