At it's closest, if it exists, it's three times the distance to Pluto.

It's also about the same size of Neptune,  actually a bit smaller.

Neptune is eight magnitude when it is at its brightest. Theoretically that puts it within human vision, just, for exceptionally keen eyed astronomers with perfect seeing. But I haven't found any account of someone who has seen Neptune.

At three times further, then it will be much less bright than Neptune. So, no I don't think anyone will see it with naked eye from Earth.

BTW, I think "planet nine" is a silly name for it. Because what if we find another planet in between it and the other planets? Or what if we change the definition of a planet? It's already been changed once and I think it might again.

Some would say that both Ceres and Pluto are planets  If so, Neptune would be planet nine and this new planet would be planet 11, or maybe a higher number than that if you also count Sedna etc as planets.

And we don't call Earth "planet 3" or Jupiter "planet 5".

So I hope they give it a new better name soon. It doesn't need to be discovered to be given a name. Nemesis and Tyche were both named although the probability seems to be that neither exists.

Mellopsia  sounds like a nice name. Google search turns up this: New planet in our solar system? Hopefully

Though - the tiny 0.007% chance of it being a coincidence seems impressive - until you realize that there are thousands of astronomers and each considers many hypotheses and a lot of data every year. With so much data and so many astronomers, you can expect a 1 in 15,000 chance every so often, even if there is nothing there at all, just from the noise.

If that was the  reason for it, then it is just a coincidence that the orbits found so far seem to suggest it exists. As we find more dwarf planets it will probably be disproved.

To be probable enough to count as almost certain in science you need a 1 in several million chance of it being a coincidence. Because 1 in 15,000 chances happen quite often in science and then get disproved.

It's our best candidate for a planet X for some time and exciting for that reason.  But is nowhere near the stage where you could call it a discovery quite yet. But I hope they do find it in the searches, it would be a fun discovery and we could learn a lot from it :).

See also my Why This New "Planet X" Is No Threat To Earth :).