original image location

In LrC, find the photo and then right-click and select Find in Explorer.

In general, your photos are wherever you put them, or wherever you told LrC to put them. If you don't know where that is, the method above will help, and you should know (at least) what disk and what parent folder to look in to find your original files.

What do you mean "Save to my external drive"? Lightroom Classic edits are automatically saved into the catalog. If you hit Ctrl-S, they are also saved to an XMP sidercar file, next to the original image. Lightroom Classic does not save an edited copy, like Photoshop or other traditional editors do. To get an edited copy (as tiff, or psd, of jpeg; you cannot save an edited raw file because then it isn't a raw file anymore) you need to export the image.