Not at all a dumb question! The argument goes that we haven't had powerful-enough telescopes (or enough dedicated observing time) to image it.

Not everyone buys this; some people think it does not exist, and the perturbed orbits of Kuiper Belt objects are just a random fluke.

"Some idea" is the problem. Basically at the orbit we think it's at, even at the relatively large size they're expecting, it would be a tiny, tiny black dot. It's the proverbial needle in a haystack, knowing which haystack it's in is only the beginning.

The scientist that found this potential planet in the old data did calculate the location where the planet should be and provided it in his article.

I'm sure there will be follow up studies and some telescopes will be pointing.

Yes we should.