Only one way to find out!
If you are reading digitally, there are several ways to deal with this. E.g. on Windows you can use KanjiTomo which will look up anything you mouse-over, or on any system you can use Mokuro which doesn’t just add furigana to most of the manga, but even makes the text selectable so you can copy it or use Yomichan (a browser plugin for really easy instant dictionary lookup).