Such a question is debatable, meaning it is subject to disagreement or doubt. If you've ever seen politicians or anyone else have a debate, then you already have a pretty good idea of what debatable means. Something is debatable if there's reason to doubt it.

What is a debatable issue called?

subject to controversy; debatable: a controversial decision. ...

What is the synonym of debated?

The words argue and discuss are common synonyms of debate.