One of the type in Bulu Monster which are effective against Dragon type monster but has a disadvantage from Earth and Spirit skills

You can see if the monster's type is Lightning by seeing a Lightning type icon in the monster's info like in the image.
Element Lightning

While in the book if you got a Lightning type monster you can see it's background like this:

Monster Book Lightning BG

Lastly, all Lightning type monsters can learn Lightning type moves and you can see if it's Lightning by the background image under the skill's info which looks like this: Skill-bg-lightning|}