My Greek family and I translate this as "Whose tower is that?" rather than "this". It highly depends on context I feel like. If we were inside the tower, it's clear they mean "this" but if we were driving by, it'd mean "that". Is this just something my family does or should "that" also be accepted?
You would need to use English question form. "To whom does this tower belong?" Then it would be correct.
But in addition, it is always a good idea to follow the format of the original sentence which is being taught as closely as possible.
"Από ποιον" means "from whom" so wouldn't fit here. "Τίνος" is already one of the accepted translations. Thanks for your input help from the community is very important to the course.
What do you mean with "this"?
Remember that nobody can see what you typed; if you have a question about a sentence, it's best to copy-and-paste your entire answer.
A link to an uploaded screenshot is even better.