The original are the woodblocks (it’s multi-colour, so I assume there were multiple blocks). Those wouldn’t show the full picture and would have been worn down, if we still had them. We don’t, though. The next best thing would be prints made by the artist.

https://www.britishmuseum.org/blog/great-wave-spot-differenc... has a nice description using wear and tear to distinguish earlier from later prints.

Edit: nowadays, artists write things like “3/50” on their prints (meaning they made fifty prints, and this is the third). That informs collectors/drives up prices for the low numbered prints.