Does svg xmlns attribute value requires protocol? Can it be https or relative?

<svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">

Can xmlns="http://www.w3.org/2000/svg" this be xmlns="https://www.w3.org/2000/svg"?

or xmlns="//www.w3.org/2000/svg"?

It's not really a URL, it's a namespace that simply happens to look like a URL. As such it must be written exactly as

xmlns="http://www.w3.org/2000/svg"

omitting the http or changing it to https will not work.

The fact that the namespace contains http does not mean in any way that the SVG file will use the http protocol for any kind of communication. The w3c could have defined the SVG namespace as foo in which case we'd all be writing xmlns="foo" and you'd not even be asking such questions.