So, finding cloudfishing spots is hard.

For regular fishing, it's a pretty safe bet that if you walk up to a body of water...heck, in many places a puddle of water...it will allow you to cast a line. Chances are it will come up with something, and if it's outside your reach (i.e. needs Gulleye) it will tell you.

Dunefishing? Here's a big obvious sand canyon in the Sagoli. Skyfishing? Most cliffs that border the Sea of Clouds are good. Hellfishing? Magma is pretty obvious and not that common.

Cloudfishing? Here's a huge map with clouds as abundant as ocean in La Noscea, but only a few spots can actually be fished from and they all looks pretty much the same. Have fun!

I *could* look up the locations on a datamining site but I'd rather they be easier to find on our own. It could be some visual effect in the worlds that distinguishes them, some skill like Arbor Call for BTN to give you a direction or text hints from an NPC or an item, or something else entirely.