Hi @stingers80-cgarchitect,
Without using a addin (API), manually the 'easiest' to find out is to export all Families.
And then start a new template (the "none" project template, imperial or metric) and drag a bunch of those families in it.
(* Depending on amount or suspected families drag x-amount or specific families in)
Next look at the Categories in the newly started project from the "none" project template, if one of the "undesired" categories comes in, it's in one of them.
Ps. it's possible the category isn't in any of the families and just created in the project, or a empty category in a family.
By Exporting the family from a project those won't be exported in the family and will be 'Cleaned' of non-used categories.
Good luck.
- Michel