Thanks for your review.
We are working hard on our documentation website. We know it has flaws, that it is not perfect nor comprehensive yet, but we have spent time over the last few weeks to improve it. Placeholders are one of the first things I've worked on.
Most notably, I recently put all the placeholders that are available for each gamemode on the corresponding page. I expected that this would make it easier to find the placeholders, but your feedback shows that it needs to be further highlighted. I'll try to improve that in the following days.
However, be aware that the theme we're using for MkDocs provides a search bar, which - I just checked - brings you the answer you're looking for if you type "bskyblock placeholders" (this is literally the first result that comes up):
https://bentobox-world.readthedocs.io/en/latest/gamemodes/BSkyBlock/Placeholders/#level-placeholders.