Are 50mm lens of any company like nikon, canon or sony same in performance? Or nikon's 50mm are better?

How do we know which company's lens are better?

No, they are not the same in performance. Not all Nikon 50mm lenses are the same in performance! The more they cost, the better the lens. No companies are "better" than another - it all depends how much you pay.

Chrisjbsc has brought up an interesting point.

Actually, the quality of the digital camera which you mount the lens AND your skills as a photographer are all part of that equation.

The most expensive Zeiss 50 mm lens will not produce any better-looking images when mounted on an entry level digital SLR when used by a novice photographer who is still learning the fundamentals of photography, lighting, and composition

That said, I have not used my Nikkor 50 mm f/1.4 lens for years. It is a great lens, but most of what I shoot requires either a wide angle or telephoto lens

Here are two samples which prove that point.

No, they are not all of the same performance. Go to photozone.de and you can compare a variety of 50mm lenses. What you'll find is that while Nikon lenses are often very good, they are also often not the best on the market too. For example, Nikon's 50mm f/1.4 is a very good lens, but the Sigma 50mm f/1.4 Art lens is better and cheaper too.

Price isn't an indicator of better performance. Just because a lens costs more doesn't mean that it's better. Take, for example, Leica's $11,000 50mm f/0.95 Noctilux. Compare the sharpness of it to a $1,000 50mm f/0.95 by other brands, and you'll see that the cheaper lens is actually sharper. But there's more to a lens than sharpness. There's color, contrast, and distortion. Some lenses produce a look that no other brand does which is one of the major selling points of Leica lenses. Some lenses produce sharpness at levels never seen before, but are criticized for having a flat, lifeless look to them. The Ottus is such a lens. While these differences are quite small, and most people would never notice them in a photograph, to the photographer they are a big deal and can help add that little bit more to a photo to help take to the next level providing that the photographer did everything right in camera.

They are not all of the same optical performance,
but for most people they can be considered to be the same.

Thirty to forty years ago, Pentax had optics nearly as good as Nikon's,
so I bought a Pentax camera.

Among the same brands, there are differences between different 50mm lens models but basically lenses with the same specs from different brands would perform almost equally. That is if you know exactly what you are doing. Picture quality depends mostly on your skill anyway so it really doesn't matter what brand you choose to use.

One other point to note is that you can't use any brand of lens with any brand of cameras body. You need to buy a lens which works with your camera - do not go for adaptors.