Can i use a nikon 50mm 1.8 lens on my samsung nx11?

What kind of adaptor do i need?

Get yourself a K-mount adapter for your NX11 (cheap on eBay!) and you have a hundreds of K-mount lenses to choose from. I would suggest the Pentax SMC-M 50mm f/1.7 as a good starting point. They're also cheap but tack sharp and a metal construction.

You would need to buy an adapter to fit your camera, the Samsung NX mount

but I strongly suggest you do not get that lens for your camera. You will not have autofocus, you might not have metering, and you will lose 1-2 stops of light