How do I create a Grid array in the inspector which lets me add data like in this image?

[HemK]

This image shows a grid that shows individual elements in an array. What data type can I use to expose elements like this?

[ShadyProductions]

By default there is no type, that can be serialized by unity in the way you want.

You have to create this yourself by creating a custom editor (PropertyDrawer is most likely what you want).

Unity - Manual: Custom Editors

Unity - Manual: Property Drawers

[xxmariofer]

there are no datatype that aare displayed like that, you will have to create your own inspector editor scripts some examples

https://stackoverflow.com/questions/49353971/how-to-create-multidimensional-array-in-unity-inspector